I have a login page , back end oracle database . when I click submit button webservice didn't work ..

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Include the full exception details, including the stack trace.

Include the relevant parts of your code, particularly the part that throws the exception.

Don't forget to indicate which line in the code the exception is thrown from.

Null exception is one of the easiest to find. Use debugger and step through the code. Find which element is null. Correct it. You're done.

If you don't succeeded, post more details (code, exact error etc) and we'll try to help. Good luck.

Try to debug and share the relevant code.