load jars without fixed version
fix to return bool values explicitly when value is bool value
Fix to return nil for NULL query output correctly
 * nil.respond_to?(:to_a) is true
 * pre-fixed code returns [] for NULL output, and it is BUG
Fix to return nil to format nil/container-values for simple value field
 * pre-fixed code raises ArgumentError for Hash/Array about non-optional value fields
  * it is unexpected: NULL is safe for many cases
 * NULL is NULL, it is SQL way