anchor.diff:        Variable? exceptionVariable, Variable? stackTraceVariable) {
       _TryContext<Variable, Type> context =
           _stack.last as _TryContext<Variable, Type>;
  -    _current = context._beforeCatch;
  +    _current = context._beforeCatch!;
       if (exceptionVariable != null) {
         _current = _current.declare(exceptionVariable, true);
       }
  
positive.code:     extends _SimpleContext<Variable, Type> {
    /// If the statement is a "try/catch" statement, the flow model representing
    /// program state at the top of any `catch` block.
    late final FlowModel<Variable, Type> _beforeCatch;
  
    /// If the statement is a "try/catch" statement, the accumulated flow model
    /// representing program state after the `try` block or one of the `catch`
    /// blocks has finished executing.  If the statement is a "try/finally"
    /// statement, the flow model representing program state after the `try` block
    /// has finished executing.
    late FlowModel<Variable, Type> _afterBodyAndCatches;
  
    _TryContext(FlowModel<Variable, Type> previous) : super(previous);
  
  
negative.code:         'No assigned variables info should have been stored for $finallyBlock');
      _TryFinallyContext<Variable, Type> context =
          _stack.removeLast() as _TryFinallyContext<Variable, Type>;
      _current = context._afterBodyAndCatches!
          .attachFinally(typeOperations, context._beforeFinally, _current);
    }
  
  