How to call Java code from soapUI?

Hi - this may be a Groovy question rather than a real soapUI question, but soapUI is the reason I am now digging into Groovy, so please bear with me:

I am trying to get a bit more information why one of my regular expressions doesn't match. Unfortunately, a statement like "assert response =~ pattern" returns essentially just yields a thumbs up/down result without any indication whatsoever why something didn't match.

I was thus trying to use some good, ol' Java code to get a bit more feedback. The PatternSyntaxException that Pattern throws if a match fails would allow to get a bit more details (error index, etc.). So I was trying a code snippet like the below:

def matches = false 

try {
   log.info('1')
   matches = java.util.regex.Pattern.matches(pattern, response)
   log.info('2: ' + matches)
} catch (java.util.regex.PatternSyntaxException psx) {
   log.info(psx.getMessage()) 
} catch (Exception ex) {
   log.info(ex)
}

assert matches

Why does this always only reach the "log.info('1')" statement and then ends in an "Error: null" popup?

I though, one of the big advantages of Groovy is that I can use plain Java code whenever I want or need to. Why does this not work here? What am I missing?