Description of problem:
Every input should be tested and/or filtered.

How reproducible:
NFS Server Settings - incorrect input should be more verbose

Steps to Reproduce:
Do something without sense. For example fill IP address field with zywe

Actual results:
Tool will not notify user, that he write it wrong.

Expected results:
In some cases you can filter input (appropriate settings on widget). Notify user about his mistake and don't let tool to traceback.

Additional info:
You can set appropriate settings. You can use signal changed and/or focus-out for text fields.