code: def _merge_before_set(self, key, existing, value, is_secret):
          
  
          def _log_before_merging(_value):
              self.logger.debug(
                  "Merging existing %s: %s with new: %s", key, existing, _value
              )
  
          def _log_after_merge(_value):
              self.logger.debug("%s merged to %s", key, _value)
  
          global_merge = getattr(self, "MERGE_ENABLED_FOR_DYNACONF", False)
  
          if isinstance(value, dict):
              local_merge = value.pop(
                  "dynaconf_merge", value.pop("dynaconf_merge_unique", None)
              )
              if global_merge or local_merge:
                  safe_value = {k: "***" for k in value} if is_secret else value
                  _log_before_merging(safe_value)
                  object_merge(existing, value)
                  safe_value = (
                      {
                          k: ("***" if k in safe_value else v)
                          for k, v in value.items()
                      }
                      if is_secret
                      else value
                  )
                  _log_after_merge(safe_value)
  
          if isinstance(value, (list, tuple)):
              local_merge = (
                  "dynaconf_merge" in value or "dynaconf_merge_unique" in value
              )
              if global_merge or local_merge:
                  value = list(value)
                  unique = False
  
                  if local_merge:
                      try:
                          value.remove("dynaconf_merge")
                      except ValueError:  # EAFP
                          value.remove("dynaconf_merge_unique")
                          unique = True
  
                  original = set(value)
                  _log_before_merging(
                      ["***" for item in value] if is_secret else value
                  )
                  object_merge(existing, value, unique=unique)
                  safe_value = (
                      ["***" if item in original else item for item in value]
                      if is_secret
                      else value
                  )
                  _log_after_merge(safe_value)
  
          return value
docs: Merge the new value being set with the existing value before set