code: def _check_defaults(self, x_only=True):
  		
  		if self.x is None:
  			self.err(self._check_defaults,
  					 "X field is not set: please specify a parameter")
  			return
  		if x_only is True:
  			return
  		if self.y is None:
  			self.err(self._check_defaults,
  					 "Y field is not set: please specify a parameter")
  			return
docs: Checks if charts defaults are set