Hey,Where is the option to validate?
As you can see in above screenshot when i click on create project then project is simply created without rejecting any URL.

Are you sure you included whitespace before the URL?

Ohh now i understand your issue.Can you please tell me where is code related to issue?I will try to fix it.
Is it in OpenRefine/main/src/com/google/refine/importers/XmlImporter.java file?

No, it is a UI issue, so it is in a Javascript file.

Here is how you can find it:

• Search for the error message "You must specify a valid web address" in the source tree: grep -R "You must specify a valid web address" .
• You will find this message in the transations: "core-index-import/warning-web-address": "You must specify a valid web address (URL) to import."
• Now search for the identifier of the message: grep -R "core-index-import/warning-web-address" ..
• The only Javascript file that contains this is ./main/webapp/modules/core/scripts/index/default-importing-sources/sources.js, so the error is coming from there.
• Open this file and look for warning-web-address.

With this method you do not need to understand OpenRefine's structure much: you can locate the code you are interested in just by following references, starting from UI text.

I think we can just add a function in UI to trim the whitespaces in the input URL before it is sent to the Regex for validation, or can we just add a trim function in the regex function?

I think we can just add a function in UI to trim the whitespaces in the input URL before it is sent to the Regex for validation, or can we just add a trim function in the regex function?

Yes am also trying to add trim function to resolve this issue :)