context.go
func (c *Context) Has(key string) bool {
	return c.Value(key) != nil
}
func (c *Context) Has(key string) bool {
	return c.Value(key) != nil
}
func ( c * Context ) Has ( key string ) bool { return c . Value ( key ) != nil }
// Has checks the existence of the key in the context.
Has checks the existence of the key in the context .