java.lang.IllegalArgumentException: Text is null

Anyone please help!

As I am executing simple login page script, application is launched but username is not entered while running the script, not sure on the below error.

Unable to set text ‘null’ of object ‘Object Repository/page_Login/input_username’

@ranjini.joshi The message means that you do not have any value (text) to pass to the input.

If you are testing web page with KS, then the format is:
WebUI.setText(findTestObject('page_Login/input_username'),"login text here")