anchor.diff:        if (returnType is InterfaceType) {
           if (returnType.classNode == handleClass) {
             diagnosticReporter.report(messageFfiLeafCallMustNotReturnHandle,
  -              node.fileOffset, 1, node.location.file);
  +              node.fileOffset, 1, node.location?.file);
           }
         }
         // Check if any of the argument types are Handle.
         for (InterfaceType param in functionType.positionalParameters) {
           if (param.classNode == handleClass) {
             diagnosticReporter.report(messageFfiLeafCallMustNotTakeHandle,
  -              node.fileOffset, 1, node.location.file);
  +              node.fileOffset, 1, node.location?.file);
           }
         }
       }
  
positive.code:               .withArguments(extended.name),
            klass.fileOffset,
            1,
            klass.location.file);
        throw _FfiStaticTypeError();
      }
    }
  
negative.code:               (exceptionalReturn is ConstantExpression &&
                    exceptionalReturn.constant is NullConstant)) {
              diagnosticReporter.report(messageFfiExceptionalReturnNull,
                  node.fileOffset, 1, node.location?.file);
              return node;
            }
  
  