code: function(propertyNamesArr, ignorePropsObj) {
  
          var propertyNamesToIgnore = [];
          for( ignoreProperty in ignorePropsObj ) {
              if( ignorePropsObj[ignoreProperty] == null ) {
                  propertyNamesToIgnore.push(ignoreProperty);
              }
          }
  
          // Remove all properties that should be ignored
          return _.difference(propertyNamesArr, propertyNamesToIgnore);
      }
docs: The purpose of this function is to take an array of property names and remove
  any names which should be ignored. For example, given the following ignorePropsObj:
  {
  name: null,
  homeTown: {
  city: null
  }
  }
  
  and the following array of property names:
  
  ['name', 'age', 'homeTown']
  
  The returned array should be ['age', 'homeTown']