class_docstr: Special KeyError to raise when requesting data from NoDB
code: def __str__(self):
      return "NoDB backend doesn't store any data. "
      "Start the Controller with a DB backend to enable resubmission / result persistence."
  
imports: import copy
  from copy import deepcopy
  from datetime import datetime
  from traitlets import Dict, Float, Integer, Unicode
  from traitlets.config.configurable import LoggingConfigurable
  from ..util import ensure_timezone
label_desc: Use image node_id 1 for calling the NoData obj's underlying member method code with example usage: obj.__str__() and returns: str