code: function isValidField(fieldObj){
          var err,
              props = _.keys(fieldObj),
              mandatoryProps = [
                  '_id',
                  'type'
              ];
  
          if(!_.isObject(fieldObj)) {
              err = new Error('Fields/Meta must be an instance of an object');
          } else {
              _.each(mandatoryProps, function(prop) {
                  if(!_.contains(props, prop)){
                      err = new Error('"' + prop + '" property not found when validating the content type.');
                  }
              });
  
              if(!err && fieldObj._id.indexOf(' ') !== -1) {
                  err = new Error('ids for fields/meta cannot have any spaces.');
              }
          }
  
          return err;
      }
docs: A field is valid if:
  1) The passed in argument must be an instance of an object
  2) All of the mandatory properties are provided
  3) The id property cannot have any spaces
  4) The type property must be in the approved list
  5) The required property must be a boolean
  @param key
  @param obj
  @returns {null}