Fix psalm issues. (#182)

* Fix psalm issues.

* Fix minor correction.

* Remove unnecessary phpdoc.

src/Schema/Schema.php

@@ -100,6 +100,8 @@ public function __construct(ConnectionInterface $db)
         $this->cache = $this->db->getSchemaCache();
     }
 
+    abstract public function createQueryBuilder(): QueryBuilder;
+
     /**
      * Resolves the table name and schema name (if any).
      *
@@ -122,11 +124,11 @@ protected function resolveTableName(string $name): TableSchema
      * This method should be overridden by child classes in order to support this feature because the default
      * implementation simply throws an exception.
      *
-     * @return void all schema names in the database, except system schemas.
+     * @return array all schema names in the database, except system schemas.
      *
      * @throws NotSupportedException if this method is not supported by the DBMS.
      */
-    protected function findSchemaNames()
+    protected function findSchemaNames(): array
     {
         throw new NotSupportedException(get_class($this) . ' does not support fetching all schema names.');
     }
@@ -139,7 +141,7 @@ protected function findSchemaNames()
      *
      * @param string $schema the schema of the tables. Defaults to empty string, meaning the current or default schema.
      *
-     * @return void all table names in the database. The names have NO schema name prefix.
+     * @return array all table names in the database. The names have NO schema name prefix.
      *
      * @throws NotSupportedException if this method is not supported by the DBMS.
      */