Added null to PDO default types (#381)

Co-authored-by: Markus Staab <[email protected]>

Author: staabm

.phpstan-dba-mysqli.cache

@@ -16,6 +16,7 @@
 use PHPStan\Type\IntegerRangeType;
 use PHPStan\Type\IntegerType;
 use PHPStan\Type\MixedType;
+use PHPStan\Type\NullType;
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\StringType;
 use PHPStan\Type\Type;
@@ -107,7 +108,7 @@ private function reduceBothType(Type $bothType, int $fetchType): Type
     public static function createDefaultType(int $fetchType): Type
     {
         // we assume native PDO is not able to return bool.
-        $pdoScalar = new UnionType([new IntegerType(), new FloatType(), new StringType()]);
+        $pdoScalar = new UnionType([new IntegerType(), new FloatType(), new StringType(), new NullType()]);
         $arrayKey = new BenevolentUnionType([new IntegerType(), new StringType()]);
 
         switch ($fetchType) {