hello
I would try something like this
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Verify TextField
${text} Get Text "your locator"
Run Keyword If '${text}' == '' Log test case passed
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OR
you can also use keyword ---
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Textfield Value Should Be
locator, expected
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where expected you can set a variable to empty
or
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Element Text Should Be locator, expected
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where expected you can set a variable to empty
upto you.
let me know if that works
_Sushant