Solve issue when using only defaultPropertyName in configuration.

[ngs-mtech]

We have found a bug when using onlye defaultPropertyName in configuration, the new propertyName is not used, falling back to DEFAULT_PROPERTY_NAME, with this fix, this situation is solved.

[ljnelson]

Thanks for your pull request! When I'm done with my "real job" I'll have a look. Obviously it looks like a simple change, but I want to check why getDefaultPropertyName() is returning null at that point.

[ljnelson]

Ah, think I found the issue. propertyName can be set to null for a variety of reasons. Therefore, I'm going to change this like so:

if (propertyName == null) {
  propertyName = this.getDefaultPropertyName();
  if (propertyName == null) {
    propertyName = DEFAULT_DEFAULT_PROPERTY_NAME;
  }
}

I'll make this change shortly and then close this pull request. Again, thanks @ngs-mtech for your PR.

[ljnelson]

I've made a change that I think will fix your behavior. Kindly review and if it works I'll close this out. Thanks again.