anchor.diff:      typeRep ??= _emitFutureOrNameNoInterop();
   
       if (type.declaredNullability == Nullability.undetermined) {
  -      throw UnsupportedError('Undetermined Nullability');
  +      _undeterminedNullabilityError(type);
       }
   
       // Emit non-nullable version directly.
  
positive.code:     // use it everywhere it appears.
      return _typeTable.nameType(type, typeRep);
    }
  
    /// Wraps [typeRep] in the appropriate wrapper for the given [nullability].
    ///
  
negative.code:     }
  
      if (type.nullability == Nullability.undetermined) {
        _undeterminedNullabilityError(type);
      }
  
      // Emit non-nullable version directly.
  