code: private Iterator<JanusGraphVertex> verticesWithProperty(JanusGraphTransaction tx, Object value) {
          return tx.query().has(propertyKey, value).vertices().iterator();
      }
docs: Look up vertices in Janus which have a property {@link JanusPreviousPropertyStep#propertyKey} with the given
  value.
  @param tx the Janus transaction to read from
  @param value the value that the property should have