code: def test_missing_field_facet():
      schema = fields.Schema(id=fields.STORED, tag=fields.ID)
      ix = RamStorage().create_index(schema)
      w = ix.writer()
      w.add_document(id=0, tag=u("alfa"))
      w.add_document(id=1, tag=u("alfa"))
      w.add_document(id=2)
      w.add_document(id=3, tag=u("bravo"))
      w.add_document(id=4)
      w.commit()
  
      with ix.searcher() as s:
          r = s.search(query.Every(), groupedby="tag")
          assert r.groups("tag") == {
              None: [2, 4],
              "bravo": [3],
              "alfa": [0, 1],
          }
  
imports: from __future__ import with_statement
  from datetime import datetime, timedelta
  import random
  from whoosh import fields, query, sorting, columns
  from whoosh.compat import u
  from whoosh.compat import permutations, xrange
  from whoosh.filedb.filestore import RamStorage
  from whoosh.util.testing import TempIndex
label_desc: Use image node_id 15 for calling a global function with example usage: test_missing_field_facet() without return types