func (c Context) MarshalText() ([]byte, error) {
	if len(c) == 0 {
		return []byte{'{', '}'}, nil
	}

	// Pre-allocate a buffer - 128 bytes is an arbitrary
	// heuristic value that seems like a good starting size.
	b := bytes.NewBuffer(make([]byte, 0, 128))
	if len(c) == 1 {
		for k, v := range c {
			b.WriteString(`{"`)
			escapeStringJSON(b, k)
			b.WriteString(`":"`)
			escapeStringJSON(b, v)