@Test
  void getCurrentName() throws JsonParseException {
    BsonParser p = Parsers.createParser("{ \"a\" : 1 }");
    assertNull(p.nextFieldName()); // START_OBJECT
    assertEquals("a", p.nextFieldName());
    assertNull(p.nextFieldName()); // value:1
    assertNull(p.nextFieldName()); // END_OBJECT
  }
Just traverse the stream without reading any values
criteria/mongo/test/org/immutables/criteria/mongo/bson4jackson/BsonParserTreeTest.java