code: def to_string(self):
          
          builder = ""
  
          index = 0
          while index < self.__len__():
              if index > 0:
                  builder = builder + ','
              builder = builder + super(ProjectionParams, self).__getitem__(index)
              index = index + 1
  
          return builder
docs: Gets a string representation of the object.
          The result is a comma-separated list of projection fields
          "field1,field2.field21,field2.field22.field221"
  
          :return: a string representation of the object.