toJson method
Converts this object into JSON format.
optimizeFor lets the program know what information to include in the
JSON data map.
- OptimizeFor.put (the default value) is used when making a data map that is being placed in a PUT request. This only includes data that has changed.
 - OptimizeFor.putFull is used when a parent object updates; so, all of the children are required to be present for the PUT request.
 - OptimizeFor.post is used when making a data map for a POST request.
 - OptimizeFor.dontOptimize is used to get all of the data contained in this object.
 
Throws InvalidValueException if action is empty and optimizeFor is
not set to OptimizeFor.dontOptimize.
Implementation
Map<String, dynamic> toJson({OptimizeFor optimizeFor = OptimizeFor.put}) {
  // Validate [action].
  if (!identical(optimizeFor, OptimizeFor.dontOptimize)) {
    if (!Validators.isValidValue(action, actionValues)) {
      if (!identical(optimizeFor, OptimizeFor.put) ||
          action != _originalAction) {
        throw InvalidValueException.withValue(action, actionValues);
      }
    }
  }
  // PUT
  if (identical(optimizeFor, OptimizeFor.put)) {
    Map<String, dynamic> toReturn = {};
    if (action != null &&
        (_originalAction == null || action != _originalAction)) {
      toReturn[ApiFields.action] = action;
    }
    return toReturn;
  }
  // PUT FULL
  if (identical(optimizeFor, OptimizeFor.putFull)) {
    return {
      ApiFields.action: action,
    };
  }
  // DEFAULT
  return {
    ApiFields.actionValues: actionValues,
    ApiFields.action: action,
  };
}