In my new code, patterns ending in ';' are seen as having an empty negative subpattern. In this case, my code treats negative numbers as if they have no prefix or suffix, causing the implicit minus sign from not being displayed.
ICU 58 behavior:
ICU 59 behavior:
'''My opinion:''' Patterns with a trailing ';' are most likely mistakes. Therefore this is not a regression we should worry about. Alternatively, we could throw an exception if the negative subpattern is empty.