code: func (c *PluginContext) Read(key ContextKey) (ContextData, error) {
  	if v, ok := c.storage[key]; ok {
  		return v, nil
  	}
  	return nil, errors.New(NotFound)
  }
docs: // Read retrieves data with the given "key" from PluginContext. If the key is not
  // present an error is returned.
  // This function is not thread safe. In multi-threaded code, lock should be
  // acquired first.