port: [#6354] isMatch adaptive expression returns error when value is null or empty string (#6426)

[github-actions[bot]]

The changes in [#6354] isMatch adaptive expression returns error when value is null or empty string (#6426) may need to be ported to maintain parity with microsoft/botbuilder-dotnet.

Fixes #6354

Description

This PR fixes the issue where the isMatch adaptive expression built-in function returns the error message regular expression is empty when the value is null or an empty string to just being processed by the evaluator instead.

Specific Changes

• Updates the IsMatch built-in function to handle empty strings and null values by the evaluator.
• Adds new unit tests to handle empty string and null values for the IsMatch function.

Testing

The following image shows the tests passing successfully.

Please review and, if necessary, port the changes.