Add helper method to handle null long values
Add helper method to handle null long values

The json may represent as NULL, which is not valid for a long value.
This method will provide a default value if it is null in json.

maurizi/otm-android,OpenTreeMap/otm-android,OpenTreeMap/otm-android,OpenTreeMap/otm-android,maurizi/otm-android,maurizi/otm-android