code: def get_mean(self) -> float:
      return float(np.mean(self._merge()))
  
imports: from abc import ABC
  from typing import Dict, Optional
  import numpy
  from .None import Indicator
  from ...util.values import to_numpy
label_desc: Use image node_id 6 for calling the _Collection obj's underlying member method code with example usage: obj.get_mean() and returns: float