code: def test_missing_overlap():
      schema = fields.Schema(
          a=fields.NUMERIC(stored=True), b=fields.KEYWORD(stored=True)
      )
      ix = RamStorage().create_index(schema)
      with ix.writer() as w:
          w.add_document(a=0, b=u("one two"))
          w.add_document(a=1)
          w.add_document(a=2, b=u("two three"))
          w.add_document(a=3)
          w.add_document(a=4, b=u("three four"))
  
      with ix.searcher() as s:
          facet = sorting.FieldFacet("b", allow_overlap=True)
          r = s.search(query.Every(), groupedby=facet)
          target = {
              "one": [0],
              "two": [0, 2],
              "three": [2, 4],
              "four": [4],
              None: [1, 3],
          }
          assert r.groups() == target
  
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 17 for calling a global function with example usage: test_missing_overlap() without return types