code: final public function removeFromMap($fieldName, $key)
      {
          $this->guardFrozenMessage();
          $field = static::schema()->getField($fieldName);
          Assertion::true($field->isAMap(), sprintf('Field [%s] must be a map.', $fieldName), $fieldName);
  
          unset($this->data[$fieldName][$key]);
  
          if (empty($this->data[$fieldName])) {
              $this->clearedFields[$fieldName] = true;
          }
  
          return $this;
      }
docs: {@inheritdoc}
  @return static