docstr: Make sure chosen objects are selected only once
docstr_tok: ["Make","sure","chosen","objects","are","selected","only","once"]
code: def validate_module(self, pipeline):
      """Make sure chosen objects are selected only once"""
      objects = set()
      if len(self.objects_list.value) == 0:
          raise ValidationError(
              "No object sets selected", self.objects_list
          )
  
      for object_name in self.objects_list.value:
          if object_name in objects:
              raise ValidationError(
                  "%s has already been selected" % object_name,
                  object_name,
              )
          objects.add(object_name)
  
imports: import centrosome.cpmorphology
  import centrosome.zernike
  import numpy
  import scipy.ndimage
  import skimage.measure
  from cellprofiler_core.constants.measurement import COLTYPE_FLOAT
  from cellprofiler_core.module import Module
  from cellprofiler_core.object import Objects
  from cellprofiler_core.setting import Divider, Binary, ValidationError
  from cellprofiler_core.setting.subscriber import LabelListSubscriber
  import cellprofiler.gui.help.content
  import cellprofiler.icons
label_desc: Use image node_id 4 for calling the MeasureObjectSizeShape obj's underlying member method code with example usage: obj.validate_module(pipeline) without return types