code: def coerce(cls, key, value):
          
  
          if not isinstance(value, MutableDict):
              if isinstance(value, dict):
                  return MutableDict(value)
              elif isinstance(value, six.string_types):
                  # Assume JSON string
                  if value:
                      return MutableDict(simplejson.loads(value, use_decimal=True))
                  else:
                      return MutableDict()  # Empty value is an empty dict
  
              # this call will raise ValueError
              return Mutable.coerce(key, value)
          else:
              return value
docs: Convert plain dictionaries to MutableDict.