anchor.diff:      }
   
       if (type.nullability == Nullability.undetermined) {
  -      throw UnsupportedError('Undetermined Nullability');
  +      _undeterminedNullabilityError(type);
       }
   
       // Emit non-nullable version directly.
  
positive.code:     typeRep ??= _emitFutureOrNameNoInterop();
  
      if (type.declaredNullability == Nullability.undetermined) {
        throw UnsupportedError('Undetermined Nullability');
      }
  
      // Emit non-nullable version directly.
  
negative.code:     // use it everywhere it appears.
      return _typeTable.nameType(type, typeRep);
    }
  
    void /* Never */ _undeterminedNullabilityError(DartType type) =>
        throw UnsupportedError(
            'Undetermined Nullability encounted while compiling '
            '${currentLibrary.fileUri}, which contains the type: $type.');
  
    /// Wraps [typeRep] in the appropriate wrapper for the given [nullability].
    ///
  