First, what's the field, text field? If it's empty than the backend java value will be null. It doesn't store empty strings.
If it's just a single space " " then you don't want to use * as it means 0 or more occurrences, so it will always be a match regardless of the value.
Can you try "^\s+", where + means 1 or more?
According to https://www.baeldung.com/java-regex-s-splus the java syntax would be "\\s+" (which makes sense since it's in double quotes), not sure, one or two backslashes one of them should work though I assume. Probably the double backslash.
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