code: func (c *Context) DefaultPostForm(key, defaultValue string) string {
  	if value, ok := c.GetPostForm(key); ok {
  		return value
  	}
  	return defaultValue
  }
docs: // DefaultPostForm returns the specified key from a POST urlencoded form or multipart form
  // when it exists, otherwise it returns the specified defaultValue string.
  // See: PostForm() and GetPostForm() for further information.