diff --git a/application/Espo/ORM/BaseEntity.php b/application/Espo/ORM/BaseEntity.php
index 3270a15023..d8cf6faf86 100644
--- a/application/Espo/ORM/BaseEntity.php
+++ b/application/Espo/ORM/BaseEntity.php
@@ -39,17 +39,24 @@ use RuntimeException;
 
 class BaseEntity implements Entity
 {
+    /**
+     * @var string|null
+     * @deprecated
+     */
     public $id = null;
 
+    /**
+     * @var string
+     */
     protected $entityType;
 
-    private $isNotNew = false;
+    private bool $isNotNew = false;
 
-    private $isSaved = false;
+    private bool $isSaved = false;
 
-    private $isFetched = false;
+    private bool $isFetched = false;
 
-    private $isBeingSaved = false;
+    private bool $isBeingSaved = false;
 
     /**
      * @todo Make private. Rename to `attributes`.
@@ -528,7 +535,7 @@ class BaseEntity implements Entity
         $preparedValue = $value;
 
         if (is_array($value)) {
-            $preparedValue = json_decode(json_encode($value));
+            $preparedValue = json_decode(json_encode($value, \JSON_THROW_ON_ERROR));
 
             if ($preparedValue instanceof stdClass) {
                 return $preparedValue;
@@ -828,8 +835,11 @@ class BaseEntity implements Entity
             return true;
         }
 
+        /** @var string */
+        $type = $this->getAttributeType($name);
+
         return !self::areValuesEqual(
-            $this->getAttributeType($name),
+            $type,
             $this->get($name),
             $this->getFetched($name),
             $this->getAttributeParam($name, 'isUnordered') ?? false
@@ -875,7 +885,7 @@ class BaseEntity implements Entity
                 $a1 = get_object_vars($v1);
                 $a2 = get_object_vars($v2);
 
-                foreach ($v1 as $key => $itemValue) {
+                foreach (get_object_vars($v1) as $key => $itemValue) {
                     if (is_object($a1[$key]) && is_object($a2[$key])) {
                         if (!self::areValuesEqual(self::JSON_OBJECT, $a1[$key], $a2[$key])) {
                             return false;
@@ -1015,6 +1025,7 @@ class BaseEntity implements Entity
      */
     protected function getEntityManager(): EntityManager
     {
+        /** @var EntityManager */
         return $this->entityManager;
     }
 
@@ -1043,6 +1054,8 @@ class BaseEntity implements Entity
 
         $copy = [];
 
+        /** @var array<int,stdClass|array|scalar|null> $value */
+
         foreach ($value as $i => $item) {
             if (is_object($item)) {
                 $copy[$i] = $this->cloneObject($item);
@@ -1074,6 +1087,8 @@ class BaseEntity implements Entity
         $copy = (object) [];
 
         foreach (get_object_vars($value) as $k => $item) {
+            /** @var stdClass|array|scalar|null $item */
+
             $key = $k;
 
             if (!is_string($key)) {
diff --git a/application/Espo/ORM/Defs/EntityDefs.php b/application/Espo/ORM/Defs/EntityDefs.php
index eb9cd843c3..382e0dea4d 100644
--- a/application/Espo/ORM/Defs/EntityDefs.php
+++ b/application/Espo/ORM/Defs/EntityDefs.php
@@ -33,16 +33,31 @@ use RuntimeException;
 
 class EntityDefs
 {
-    private $data;
+    /**
+     * @var array<string,array<string,mixed>>
+     */
+    private array $data;
 
-    private $name;
+    private string $name;
 
+    /**
+     * @var array<string,?AttributeDefs>
+     */
     private $attributeCache = [];
 
+    /**
+     * @var array<string,?RelationDefs>
+     */
     private $relationCache = [];
 
+    /**
+     * @var array<string,?IndexDefs>
+     */
     private $indexCache = [];
 
+    /**
+     * @var array<string,?FieldDefs>
+     */
     private $fieldCache = [];
 
     private function __construct()
@@ -224,6 +239,7 @@ class EntityDefs
             throw new RuntimeException("Attribute '{$name}' does not exist.");
         }
 
+        /** @var AttributeDefs */
         return $this->attributeCache[$name];
     }
 
@@ -239,6 +255,7 @@ class EntityDefs
             throw new RuntimeException("Relation '{$name}' does not exist.");
         }
 
+        /** @var RelationDefs */
         return $this->relationCache[$name];
     }
 
@@ -254,6 +271,7 @@ class EntityDefs
             throw new RuntimeException("Index '{$name}' does not exist.");
         }
 
+        /** @var IndexDefs */
         return $this->indexCache[$name];
     }
 
@@ -269,6 +287,7 @@ class EntityDefs
             throw new RuntimeException("Field '{$name}' does not exist.");
         }
 
+        /** @var FieldDefs */
         return $this->fieldCache[$name];
     }
 
diff --git a/application/Espo/ORM/EntityCollection.php b/application/Espo/ORM/EntityCollection.php
index c3d9dfe867..eaffdef794 100644
--- a/application/Espo/ORM/EntityCollection.php
+++ b/application/Espo/ORM/EntityCollection.php
@@ -221,6 +221,8 @@ class EntityCollection implements Collection, Iterator, Countable, ArrayAccess,
             throw new RuntimeException("Can't build from array. EntityFactory was not passed to the constructor.");
         }
 
+        assert($this->entityType !== null);
+
         $entity = $this->entityFactory->create($this->entityType);
 
         $entity->set($dataArray);
diff --git a/application/Espo/ORM/EntityManager.php b/application/Espo/ORM/EntityManager.php
index 223840c5fd..1376255669 100644
--- a/application/Espo/ORM/EntityManager.php
+++ b/application/Espo/ORM/EntityManager.php
@@ -151,9 +151,12 @@ class EntityManager
         $this->initLocker();
     }
 
+    /**
+     * @todo Use factory.
+     */
     private function initQueryComposer(): void
     {
-        $platform = $this->databaseParams->getPlatform();
+        $platform = $this->databaseParams->getPlatform() ?? 'Dummy';
 
         $className = 'Espo\\ORM\\QueryComposer\\' . ucfirst($platform) . 'QueryComposer';
 
@@ -161,17 +164,23 @@ class EntityManager
             throw new RuntimeException("Query composer for '{$platform}' platform does not exits.");
         }
 
-        $this->queryComposer = new $className(
+        /** @var QueryComposer */
+        $queryComposer = new $className(
             $this->pdoProvider->get(),
             $this->entityFactory,
             $this->metadata,
             $this->functionConverterFactory
         );
+
+        $this->queryComposer = $queryComposer;
     }
 
+    /**
+     * @todo Use factory.
+     */
     private function initLocker(): void
     {
-        $platform = $this->databaseParams->getPlatform();
+        $platform = $this->databaseParams->getPlatform() ?? 'Dummy';
 
         $className = 'Espo\\ORM\\Locker\\' . ucfirst($platform) . 'Locker';
 
@@ -179,7 +188,10 @@ class EntityManager
             $className = BaseLocker::class;
         }
 
-        $this->locker = new $className($this->pdoProvider->get(), $this->queryComposer, $this->transactionManager);
+        /** @var Locker */
+        $locker = new $className($this->pdoProvider->get(), $this->queryComposer, $this->transactionManager);
+
+        $this->locker = $locker;
     }
 
     /**
@@ -223,7 +235,8 @@ class EntityManager
         if ($name === self::RDB_MAPPER_NAME) {
             $className = $this->getRDBMapperClassName();
 
-            $this->mappers[$name] = new $className(
+            /** @var Mapper */
+            $mapper = new $className(
                 $this->pdoProvider->get(),
                 $this->entityFactory,
                 $this->collectionFactory,
@@ -232,6 +245,8 @@ class EntityManager
                 $this->sqlExecutor
             );
 
+            $this->mappers[$name] = $mapper;
+
             return;
         }
 
@@ -244,7 +259,7 @@ class EntityManager
 
     private function getRDBMapperClassName(): string
     {
-        $platform = $this->databaseParams->getPlatform();
+        $platform = $this->databaseParams->getPlatform() ?? 'Dummy';
 
         $className = 'Espo\\ORM\\Mapper\\' . ucfirst($platform) . 'Mapper';
 
@@ -277,6 +292,7 @@ class EntityManager
      */
     public function getNewEntity(string $entityType): Entity
     {
+        /** @var Entity */
         return $this->getEntity($entityType);
     }
 
@@ -352,7 +368,7 @@ class EntityManager
      */
     public function createEntity(string $entityType, $data = [], array $options = []): Entity
     {
-        $entity = $this->getEntity($entityType);
+        $entity = $this->getNewEntity($entityType);
 
         $entity->set($data);
 
@@ -384,7 +400,13 @@ class EntityManager
             $this->repositoryHash[$entityType] = $this->repositoryFactory->create($entityType);
         }
 
-        return $this->repositoryHash[$entityType];
+        $repository = $this->repositoryHash[$entityType];
+
+        if (!$repository instanceof RDBRepository) {
+            throw new RuntimeException("Repository '{$entityType}' is not RDB.");
+        }
+
+        return $repository;
     }
 
     /**
diff --git a/application/Espo/ORM/Mapper/BaseMapper.php b/application/Espo/ORM/Mapper/BaseMapper.php
index 1da63fdd3e..7e3562d250 100644
--- a/application/Espo/ORM/Mapper/BaseMapper.php
+++ b/application/Espo/ORM/Mapper/BaseMapper.php
@@ -55,46 +55,25 @@ use RuntimeException;
  */
 class BaseMapper implements RDBMapper
 {
-    const ATTRIBUTE_DELETED = 'deleted';
+    protected const ATTRIBUTE_DELETED = 'deleted';
 
-    protected $fieldsMapCache = [];
+    protected array $fieldsMapCache = [];
 
-    protected $aliasesCache = [];
+    protected array $aliasesCache = [];
 
-    /**
-     * @var PDO
-     */
-    protected $pdo;
+    protected PDO $pdo;
 
-    /**
-     * @var EntityFactory
-     */
-    protected $entityFactory;
+    protected EntityFactory $entityFactory;
 
-    /**
-     * @var CollectionFactory
-     */
-    protected $collectionFactory;
+    protected CollectionFactory $collectionFactory;
 
-    /**
-     * @var QueryComposer
-     */
-    protected $queryComposer;
+    protected QueryComposer $queryComposer;
 
-    /**
-     * @var Metadata
-     */
-    protected $metadata;
+    protected Metadata $metadata;
 
-    /**
-     * @var SqlExecutor
-     */
-    protected $sqlExecutor;
+    protected SqlExecutor $sqlExecutor;
 
-    /**
-     * @var Helper
-     */
-    protected $helper;
+    protected Helper $helper;
 
     public function __construct(
         PDO $pdo,
@@ -121,6 +100,10 @@ class BaseMapper implements RDBMapper
     {
         $entityType = $select->getFrom();
 
+        if ($entityType === null) {
+            throw new RuntimeException("No entity type.");
+        }
+
         $entity = $this->entityFactory->create($entityType);
 
         $sql = $this->queryComposer->compose($select);
@@ -191,6 +174,10 @@ class BaseMapper implements RDBMapper
     {
         $entityType = $select->getFrom();
 
+        if ($entityType === null) {
+            throw new RuntimeException("No entity type.");
+        }
+
         $sql = $this->queryComposer->compose($select);
 
         return $this->selectBySqlInternal($entityType, $sql);
@@ -213,6 +200,10 @@ class BaseMapper implements RDBMapper
     {
         $entityType = $select->getFrom();
 
+        if ($entityType === null) {
+            throw new RuntimeException("No entity type.");
+        }
+
         $entity = $this->entityFactory->create($entityType);
 
         if (empty($aggregation) || !$entity->hasAttribute($aggregationBy)) {
@@ -299,6 +290,7 @@ class BaseMapper implements RDBMapper
 
         switch ($relType) {
             case Entity::BELONGS_TO:
+                /** @var Entity $relEntity */
 
                 $params['whereClause'][$foreignKey] = $entity->get($key);
                 $params['offset'] = 0;
@@ -352,6 +344,8 @@ class BaseMapper implements RDBMapper
 
                 $resultDataList = [];
 
+                /** @var Entity $relEntity */
+
                 $params['from'] = $relEntity->getEntityType();
 
                 $sql = $this->queryComposer->compose(Select::fromRaw($params));
@@ -394,6 +388,8 @@ class BaseMapper implements RDBMapper
                     $params['select'] ?? []
                 );
 
+                /** @var Entity $relEntity */
+
                 $params['from'] = $relEntity->getEntityType();
 
                 $sql = $this->queryComposer->compose(Select::fromRaw($params));
@@ -1155,6 +1151,8 @@ class BaseMapper implements RDBMapper
 
                 $where[static::ATTRIBUTE_DELETED] = false;
 
+                /** @var Entity $relEntity */
+
                 $sql = $this->queryComposer->compose(
                     Update::fromRaw([
                         'from' => $relEntity->getEntityType(),
diff --git a/application/Espo/ORM/Metadata.php b/application/Espo/ORM/Metadata.php
index abdcdcb88e..dd6baa9ff7 100644
--- a/application/Espo/ORM/Metadata.php
+++ b/application/Espo/ORM/Metadata.php
@@ -123,9 +123,12 @@ class Metadata
         return array_keys($this->data);
     }
 
+    /**
+     * @param string[]|string|null $key
+     */
     private static function getValueByKey(array $data, $key = null, $default = null)
     {
-        if (!is_string($key) && !is_array($key) && !is_null($key)) {
+        if (!is_string($key) && !is_array($key) && !is_null($key)) { /** @phpstan-ignore-line */
             throw new InvalidArgumentException();
         }
 
@@ -139,6 +142,8 @@ class Metadata
             $path = explode('.', $key);
         }
 
+        /** @var string[] $path */
+
         $item = $data;
 
         foreach ($path as $k) {
diff --git a/application/Espo/ORM/PDO/DefaultPDOProvider.php b/application/Espo/ORM/PDO/DefaultPDOProvider.php
index 8e1d0fe1b4..977743ed72 100644
--- a/application/Espo/ORM/PDO/DefaultPDOProvider.php
+++ b/application/Espo/ORM/PDO/DefaultPDOProvider.php
@@ -54,6 +54,8 @@ class DefaultPDOProvider implements PDOProvider
             $this->intPDO();
         }
 
+        assert($this->pdo !== null);
+
         return $this->pdo;
     }
 
diff --git a/application/Espo/ORM/PDO/Options.php b/application/Espo/ORM/PDO/Options.php
index 1e03cf0206..4a29ac0960 100644
--- a/application/Espo/ORM/PDO/Options.php
+++ b/application/Espo/ORM/PDO/Options.php
@@ -36,7 +36,7 @@ use PDO;
 class Options
 {
     /**
-     * @return array<string, mixed>
+     * @return array<int, mixed>
      */
     public static function getOptionsFromDatabaseParams(DatabaseParams $databaseParams): array
     {
diff --git a/application/Espo/ORM/Query/SelectBuilder.php b/application/Espo/ORM/Query/SelectBuilder.php
index 3fd2ff0c59..8ebbde1b31 100644
--- a/application/Espo/ORM/Query/SelectBuilder.php
+++ b/application/Espo/ORM/Query/SelectBuilder.php
@@ -242,8 +242,8 @@ class SelectBuilder implements Builder
      * * `having(array $clause)`
      * * `having(string $key, string $value)`
      *
-     * @param WhereItem|array|string $clause A key or where clause.
-     * @param array|string|null $value A value. Omitted if the first argument is not string.
+     * @param WhereItem|array<mixed,mixed>|string $clause A key or where clause.
+     * @param mixed[]|scalar|null $value A value. Omitted if the first argument is not string.
      */
     public function having($clause, $value = null): self
     {
diff --git a/application/Espo/ORM/Query/SelectingBuilderTrait.php b/application/Espo/ORM/Query/SelectingBuilderTrait.php
index 25ee6f852e..874def7a78 100644
--- a/application/Espo/ORM/Query/SelectingBuilderTrait.php
+++ b/application/Espo/ORM/Query/SelectingBuilderTrait.php
@@ -49,8 +49,8 @@ trait SelectingBuilderTrait
      * * `where(array $clause)`
      * * `where(string $key, string $value)`
      *
-     * @param WhereItem|array|string $clause A key or where clause.
-     * @param array|string|null $value A value. Omitted if the first argument is not string.
+     * @param WhereItem|array<mixed,mixed>|string $clause A key or where clause.
+     * @param mixed[]|scalar|null $value A value. Omitted if the first argument is not string.
      */
     public function where($clause, $value = null): self
     {
diff --git a/application/Espo/ORM/QueryComposer/BaseQueryComposer.php b/application/Espo/ORM/QueryComposer/BaseQueryComposer.php
index fd9ddeb5c5..a2d2ecac17 100644
--- a/application/Espo/ORM/QueryComposer/BaseQueryComposer.php
+++ b/application/Espo/ORM/QueryComposer/BaseQueryComposer.php
@@ -613,6 +613,7 @@ abstract class BaseQueryComposer implements QueryComposer
             $selectPart = $this->getSelectPart($entity, $params);
 
             $additionalSelectPart = $this->getAdditionalSelect($entity, $params);
+
             if ($additionalSelectPart) {
                 $selectPart .= $additionalSelectPart;
             }
@@ -630,7 +631,11 @@ abstract class BaseQueryComposer implements QueryComposer
             $params['select'] = [];
 
             $selectPart = $this->getAggregationSelectPart(
-                $entity, $params['aggregation'], $params['aggregationBy'], $aggregationDistinct, $params
+                $entity,
+                $params['aggregation'],
+                $params['aggregationBy'],
+                $aggregationDistinct,
+                $params
             );
         }
 
@@ -639,6 +644,7 @@ abstract class BaseQueryComposer implements QueryComposer
             if ($wherePart) {
                 $wherePart .= ' ';
             }
+
             $wherePart .= $params['customWhere'];
         }
 
@@ -679,6 +685,9 @@ abstract class BaseQueryComposer implements QueryComposer
             $fromPart = '(' . $this->composeSelecting($fromQuery) . ')';
         }
 
+        /** @var string $selectPart */
+        /** @var string $fromAlias */
+
         if ($isAggregation) {
             $sql = $this->composeSelectQuery(
                 $fromPart,
@@ -880,13 +889,16 @@ abstract class BaseQueryComposer implements QueryComposer
         return $selectPart;
     }
 
+    /**
+     * @param string[] $argumentPartList
+     */
     protected function getFunctionPart(
         string $function,
         string $part,
         array $params,
         string $entityType,
-        bool $distinct = false,
-        ?array $argumentPartList = null
+        bool $distinct,
+        array $argumentPartList = []
     ): string {
 
         $isBuiltIn = in_array($function, Functions::FUNCTION_LIST);
@@ -1084,6 +1096,8 @@ abstract class BaseQueryComposer implements QueryComposer
 
     private function getFunctionPartFromFactory(string $function, array $argumentPartList): string
     {
+        assert($this->functionConverterFactory !== null);
+
         $obj = $this->functionConverterFactory->create($function);
 
         return $obj->convert(...$argumentPartList);
@@ -1233,7 +1247,16 @@ abstract class BaseQueryComposer implements QueryComposer
         }
 
         if ($function) {
-            $part = $this->getFunctionPart($function, $part, $params, $entityType, $distinct, $argumentPartList);
+            /** @var string[] $argumentPartList */
+
+            $part = $this->getFunctionPart(
+                $function,
+                $part,
+                $params,
+                $entityType,
+                $distinct,
+                $argumentPartList
+            );
         }
 
         return $part;
@@ -1408,6 +1431,7 @@ abstract class BaseQueryComposer implements QueryComposer
                 $modifiedOrder[] = $newItem;
             }
 
+            /** @var string */
             $part = $this->getOrderExpressionPart($entity, $modifiedOrder, null, $params, true);
 
             return $part;
@@ -1527,7 +1551,7 @@ abstract class BaseQueryComposer implements QueryComposer
         if (!empty($defs['joins'])) {
             foreach ($defs['joins'] as $j) {
                 $jAlias = $this->obtainJoinAlias($j);
-                $jAlias = str_replace('{alias}', $alias, $jAlias);
+                $jAlias = str_replace('{alias}', $alias ?? '', $jAlias);
 
                 if (isset($j[1])) {
                     $j[1] = $jAlias;
@@ -1567,7 +1591,7 @@ abstract class BaseQueryComposer implements QueryComposer
             $params['extraAdditionalSelect'] = $params['extraAdditionalSelect'] ?? [];
 
             foreach ($defs['additionalSelect'] as $value) {
-                $value = str_replace('{alias}', $alias, $value);
+                $value = str_replace('{alias}', $alias ?? '', $value);
                 $value = str_replace('{attribute}', $attribute, $value);
 
                 if (!in_array($value, $params['extraAdditionalSelect'])) {
@@ -1725,6 +1749,9 @@ abstract class BaseQueryComposer implements QueryComposer
         return $selectPart;
     }
 
+    /**
+     * @param string|string[] $attribute
+     */
     protected function getSelectPartItemPair(?Entity $entity, array &$params, $attribute): ?array
     {
         $maxTextColumnsLength = $params['maxTextColumnsLength'] ?? null;
@@ -1733,7 +1760,7 @@ abstract class BaseQueryComposer implements QueryComposer
 
         $attributeType = null;
 
-        if (!is_array($attribute) && !is_string($attribute)) {
+        if (!is_array($attribute) && !is_string($attribute)) { /** @phpstan-ignore-line */
             throw new RuntimeException("ORM Query: Bad select item.");
         }
 
@@ -1759,7 +1786,7 @@ abstract class BaseQueryComposer implements QueryComposer
         }
 
         // @todo Make VALUE: usage deprecated.
-        if (stripos($expression, 'VALUE:') === 0) {
+        if (is_string($expression) && stripos($expression, 'VALUE:') === 0) {
             $part = $this->quote(
                 substr($expression, 6)
             );
@@ -1768,6 +1795,10 @@ abstract class BaseQueryComposer implements QueryComposer
         }
 
         if (!$entity) {
+            if (!is_string($expression)) {
+                throw new RuntimeException();
+            }
+
             return [
                 $this->convertComplexExpression(null, $expression, false, $params),
                 $alias
@@ -1804,6 +1835,10 @@ abstract class BaseQueryComposer implements QueryComposer
             return [$part, $alias];
         }
 
+        if (!is_string($attribute)) {
+            throw new RuntimeException();
+        }
+
         if (!$entity->hasAttribute($attribute)) {
             $expression = $attribute;
 
@@ -2048,7 +2083,7 @@ abstract class BaseQueryComposer implements QueryComposer
         if (strpos($orderBy, 'LIST:') === 0) {
             list($l, $field, $list) = explode(':', $orderBy);
 
-            $fieldPath = $this->getAttributePathForOrderBy($entity, $field, $params);
+            $fieldPath = $this->getAttributePathForOrderBy($entity, $field, $params ?? []);
 
             $listQuoted = [];
 
@@ -2088,7 +2123,7 @@ abstract class BaseQueryComposer implements QueryComposer
             return $this->getAttributeOrderSql($entity, $orderBy, $params, $order);
         }
 
-        $fieldPath = $this->getAttributePathForOrderBy($entity, $orderBy, $params);
+        $fieldPath = $this->getAttributePathForOrderBy($entity, $orderBy, $params ?? []);
 
         if (!$fieldPath) {
             throw new LogicException("Could not handle 'order' for '".$entity->getEntityType()."'.");
@@ -2697,7 +2732,7 @@ abstract class BaseQueryComposer implements QueryComposer
      */
     public function sanitize(string $string): string
     {
-        return preg_replace('/[^A-Za-z0-9_]+/', '', $string);
+        return preg_replace('/[^A-Za-z0-9_]+/', '', $string) ?? '';
     }
 
     /**
@@ -2707,7 +2742,7 @@ abstract class BaseQueryComposer implements QueryComposer
      */
     public function sanitizeSelectAlias(string $string): string
     {
-        $string = preg_replace('/[^A-Za-z\r\n0-9_:\'" .,\-\(\)]+/', '', $string);
+        $string = preg_replace('/[^A-Za-z\r\n0-9_:\'" .,\-\(\)]+/', '', $string) ?? '';
 
         if (strlen($string) > 256) {
             $string = substr($string, 0, 256);
@@ -2718,7 +2753,7 @@ abstract class BaseQueryComposer implements QueryComposer
 
     protected function sanitizeIndexName(string $string): string
     {
-        return preg_replace('/[^A-Za-z0-9_]+/', '', $string);
+        return preg_replace('/[^A-Za-z0-9_]+/', '', $string) ?? '';
     }
 
     protected function getJoinsTypePart(
diff --git a/application/Espo/ORM/QueryComposer/MysqlQueryComposer.php b/application/Espo/ORM/QueryComposer/MysqlQueryComposer.php
index be306b6769..4580db2635 100644
--- a/application/Espo/ORM/QueryComposer/MysqlQueryComposer.php
+++ b/application/Espo/ORM/QueryComposer/MysqlQueryComposer.php
@@ -29,9 +29,8 @@
 
 namespace Espo\ORM\QueryComposer;
 
-use Espo\ORM\{
-    Query\LockTable as LockTableQuery,
-};
+use Espo\ORM\Query\LockTable as LockTableQuery;
+
 use LogicException;
 
 class MysqlQueryComposer extends BaseQueryComposer
diff --git a/application/Espo/ORM/Repository/RDBRelation.php b/application/Espo/ORM/Repository/RDBRelation.php
index 78a3b2f828..10ac093454 100644
--- a/application/Espo/ORM/Repository/RDBRelation.php
+++ b/application/Espo/ORM/Repository/RDBRelation.php
@@ -49,21 +49,21 @@ use RuntimeException;
  */
 class RDBRelation
 {
-    private $entityManager;
+    private EntityManager $entityManager;
 
-    private $hookMediator;
+    private HookMediator $hookMediator;
 
-    private $entity;
+    private Entity $entity;
 
-    private $entityType;
+    private string $entityType;
 
-    private $foreignEntityType = null;
+    private ?string $foreignEntityType = null;
 
-    private $relationName;
+    private string $relationName;
 
-    private $relationType = null;
+    private ?string $relationType = null;
 
-    private $noBuilder = false;
+    private bool $noBuilder = false;
 
     public function __construct(
         EntityManager $entityManager,
@@ -178,6 +178,7 @@ class RDBRelation
     public function findOne(): ?Entity
     {
         if ($this->isBelongsToParentType()) {
+            /** @var ?Entity */
             return $this->getMapper()->selectRelated($this->entity, $this->relationName);
         }
 
@@ -445,7 +446,10 @@ class RDBRelation
             throw new RuntimeException();
         }
 
-        $seed = $this->entityManager->getEntityFactory()->create($this->foreignEntityType);
+        /** @var string */
+        $foreignEntityType = $this->foreignEntityType;
+
+        $seed = $this->entityManager->getEntityFactory()->create($foreignEntityType);
 
         $seed->set('id', $id);
 
@@ -465,7 +469,10 @@ class RDBRelation
             throw new RuntimeException();
         }
 
-        $seed = $this->entityManager->getEntityFactory()->create($this->foreignEntityType);
+        /** @var string */
+        $foreignEntityType = $this->foreignEntityType;
+
+        $seed = $this->entityManager->getEntityFactory()->create($foreignEntityType);
 
         $seed->set('id', $id);
 
@@ -485,7 +492,11 @@ class RDBRelation
             throw new RuntimeException();
         }
 
-        $seed = $this->entityManager->getEntityFactory()->create($this->foreignEntityType);
+        /** @var string */
+        $foreignEntityType = $this->foreignEntityType;
+
+        $seed = $this->entityManager->getEntityFactory()->create($foreignEntityType);
+
         $seed->set('id', $id);
 
         $this->updateColumns($seed, $columnData);
@@ -551,7 +562,13 @@ class RDBRelation
             throw new RuntimeException("Can't update not many-to-many relation.");
         }
 
-        $this->getMapper()->updateRelationColumns($this->entity, $this->relationName, $entity->getId(), $columnData);
+        $id = $entity->getId();
+
+        if ($id === null) {
+            throw new RuntimeException("Entity w/o ID.");
+        }
+
+        $this->getMapper()->updateRelationColumns($this->entity, $this->relationName, $id, $columnData);
     }
 
     /**
@@ -567,7 +584,13 @@ class RDBRelation
             throw new RuntimeException("Can't get a column of not many-to-many relation.");
         }
 
-        return $this->getMapper()->getRelationColumn($this->entity, $this->relationName, $entity->getId(), $column);
+        $id = $entity->getId();
+
+        if ($id === null) {
+            throw new RuntimeException("Entity w/o ID.");
+        }
+
+        return $this->getMapper()->getRelationColumn($this->entity, $this->relationName, $id, $column);
     }
 
     private function beforeRelate(Entity $entity, ?array $columnData, array $options): void
diff --git a/application/Espo/ORM/Repository/RDBRepository.php b/application/Espo/ORM/Repository/RDBRepository.php
index d1df778337..fe2a1fe088 100644
--- a/application/Espo/ORM/Repository/RDBRepository.php
+++ b/application/Espo/ORM/Repository/RDBRepository.php
@@ -60,7 +60,7 @@ class RDBRepository implements Repository
 
     protected EntityFactory $entityFactory;
 
-    protected ?HookMediator $hookMediator;
+    protected HookMediator $hookMediator;
 
     protected RDBTransactionManager $transactionManager;
 
@@ -320,16 +320,28 @@ class RDBRepository implements Repository
         }
 
         if ($type === Entity::MANY_MANY && count($additionalColumns)) {
+            if ($select === null) {
+                throw new RuntimeException();
+            }
+
             $select = $this->applyRelationAdditionalColumns($entity, $relationName, $additionalColumns, $select);
         }
 
         // @todo Get rid of 'additionalColumnsConditions' usage. Use 'whereClause' instead.
         if ($type === Entity::MANY_MANY && count($additionalColumnsConditions)) {
+            if ($select === null) {
+                throw new RuntimeException();
+            }
+
             $select = $this->applyRelationAdditionalColumnsConditions(
-                $entity, $relationName, $additionalColumnsConditions, $select
+                $entity,
+                $relationName,
+                $additionalColumnsConditions,
+                $select
             );
         }
 
+        /** @var Collection<TEntity>|TEntity|null */
         $result = $this->getMapper()->selectRelated($entity, $relationName, $select);
 
         if ($result instanceof SthCollection) {
@@ -373,8 +385,15 @@ class RDBRepository implements Repository
         }
 
         if ($type === Entity::MANY_MANY && count($additionalColumnsConditions)) {
+            if ($select === null) {
+                throw new RuntimeException();
+            }
+
             $select = $this->applyRelationAdditionalColumnsConditions(
-                $entity, $relationName, $additionalColumnsConditions, $select
+                $entity,
+                $relationName,
+                $additionalColumnsConditions,
+                $select
             );
         }
 
diff --git a/application/Espo/ORM/Repository/RDBSelectBuilder.php b/application/Espo/ORM/Repository/RDBSelectBuilder.php
index 2c0c2cc4f1..e233d631c3 100644
--- a/application/Espo/ORM/Repository/RDBSelectBuilder.php
+++ b/application/Espo/ORM/Repository/RDBSelectBuilder.php
@@ -57,9 +57,9 @@ class RDBSelectBuilder
     private SelectBuilder $builder;
 
     /**
-     * @var RDBRepository<TEntity>|null
+     * @var RDBRepository<TEntity>
      */
-    private ?RDBRepository $repository = null;
+    private RDBRepository $repository;
 
     private bool $returnSthCollection = false;
 
@@ -67,7 +67,10 @@ class RDBSelectBuilder
     {
         $this->entityManager = $entityManager;
 
-        $this->repository = $this->entityManager->getRepository($entityType);
+        /** @var RDBRepository<TEntity> */
+        $repository = $this->entityManager->getRepository($entityType);
+
+        $this->repository = $repository;
 
         if ($query && $query->getFrom() !== $entityType) {
             throw new RuntimeException("SelectBuilder: Passed query doesn't match the entity type.");
@@ -114,6 +117,7 @@ class RDBSelectBuilder
 
         if ($params !== null) { // @todo Remove.
             $query = $this->getMergedParams($params);
+
             $builder = $this->repository->clone($query);
         }
 
diff --git a/application/Espo/ORM/SthCollection.php b/application/Espo/ORM/SthCollection.php
index 658dbe4ceb..e841cbf994 100644
--- a/application/Espo/ORM/SthCollection.php
+++ b/application/Espo/ORM/SthCollection.php
@@ -37,6 +37,7 @@ use Countable;
 use Traversable;
 use PDO;
 use PDOStatement;
+use RuntimeException;
 
 /**
  * Reasonable to use when selecting a large number of records.
@@ -106,6 +107,7 @@ class SthCollection implements Collection, IteratorAggregate, Countable
 
     private function getQuery(): SelectQuery
     {
+        /** @var SelectQuery */
         return $this->query;
     }
 
@@ -145,6 +147,8 @@ class SthCollection implements Collection, IteratorAggregate, Countable
     {
         $this->executeQueryIfNotExecuted();
 
+        assert($this->sth !== null);
+
         return $this->sth->fetch(PDO::FETCH_ASSOC);
     }
 
@@ -152,6 +156,8 @@ class SthCollection implements Collection, IteratorAggregate, Countable
     {
         $this->executeQueryIfNotExecuted();
 
+        assert($this->sth !== null);
+
         $rowCount = $this->sth->rowCount();
 
         // MySQL may not return a row count for select queries.
@@ -193,6 +199,7 @@ class SthCollection implements Collection, IteratorAggregate, Countable
 
     public function getValueMapList(): array
     {
+        /** @var \stdClass[] */
         return $this->toArray(true);
     }
 
@@ -221,7 +228,13 @@ class SthCollection implements Collection, IteratorAggregate, Countable
         /** @var self<Entity> */
         $obj = new self($entityManager);
 
-        $obj->entityType = $query->getFrom();
+        $entityType = $query->getFrom();
+
+        if ($entityType === null) {
+            throw new RuntimeException("Query w/o entity type.");
+        }
+
+        $obj->entityType = $entityType;
         $obj->query = $query;
 
         return $obj;
diff --git a/application/Espo/ORM/Value/GeneralAttributeExtractor.php b/application/Espo/ORM/Value/GeneralAttributeExtractor.php
index 3b115f03b9..36aa95b48c 100644
--- a/application/Espo/ORM/Value/GeneralAttributeExtractor.php
+++ b/application/Espo/ORM/Value/GeneralAttributeExtractor.php
@@ -39,7 +39,7 @@ class GeneralAttributeExtractor
     private AttributeExtractorFactory $factory;
 
     /**
-     * @var array<string,AttributeExtractorFactory<object>>
+     * @var array<string,AttributeExtractor<object>>
      */
     private $cache = [];
 
diff --git a/application/Espo/ORM/Value/GeneralValueFactory.php b/application/Espo/ORM/Value/GeneralValueFactory.php
index c9451035c8..788fa5aaba 100644
--- a/application/Espo/ORM/Value/GeneralValueFactory.php
+++ b/application/Espo/ORM/Value/GeneralValueFactory.php
@@ -38,7 +38,7 @@ class GeneralValueFactory
     private ValueFactoryFactory $valueFactoryFactory;
 
     /**
-     * @var array<string,ValueFactory>
+     * @var array<string,?ValueFactory>
      */
     private array $factoryCache = [];
 
@@ -74,6 +74,7 @@ class GeneralValueFactory
             throw new RuntimeException("No value-object factory for '{$entityType}.{$field}'.");
         }
 
+        /** @var ValueFactory */
         return $factory->createFromEntity($entity, $field);
     }