Only vbc's On Error lowering produces this filter; structured
Catch...When filters call SetProjectError and never reach it. Roslyn
emits it from a single code path with System.Exception as the type, and
legacy vbc output has the same shape, so there is no chain of unknown
conjuncts to walk. The transform runs before the expression transforms
canonicalize comparisons, so the filter still compares with cgt against
ldnull and cgt.un against zero: the ldnull comparison is fixed up first,
and MatchCompUnsignedZero accepts both the unsigned and canonical form.
Assisted-by: Claude:claude-opus-5:Claude Code
Siegfried Pammer