// a precondition failed.
func IsPreconditionFailed(err error) bool {
	_, ok := err.(ErrPreconditionFailed)
	return ok
}

type ErrPreconditionFailed struct {
	message string
}

func NewErrPreconditionFailed(target map[string]interface{}) ErrPreconditionFailed {
	s := fmt.Sprintf("precondition failed for: %v", target)
	return ErrPreconditionFailed{s}
}

func (err ErrPreconditionFailed) Error() string {

	}
	meetPreconditions, err := meetPreconditions(patchMap, fns...)
	if err != nil {
		return nil, err
	}
	if !meetPreconditions {
		return nil, mergepatch.NewErrPreconditionFailed(patchMap)
	}

	return patch, nil
}

// keepOrDeleteNullInJsonPatch takes a json-encoded byte array and a boolean.
// It returns a filtered object and its corresponding json-encoded byte array.

	if err != nil {
		return nil, err
	}

	// Apply the preconditions to the patch, and return an error if any of them fail.
	for _, fn := range fns {
		if !fn(patchMap) {
			return nil, mergepatch.NewErrPreconditionFailed(patchMap)
		}
	}

	return patchMap, nil
}

// Returns a (recursive) strategic merge patch that yields modified when applied to original.
// Including: