code: private static function getNullableNames(string $table): array
      {
          if (self::$nullablesCache === null || !array_key_exists($table, self::$nullablesCache))
              self::getNullables($table);
  
          return array_keys(self::$nullablesCache[$table]);
      }
docs: Gets all of the names of NULL-able columns from the specified table schema.
  
  @param string $table
  @return array
  @throws DatabaseConnectionException