"(MISSING)" when encoding values

When encoding values, an error occurs. The value "@" is not encoded and just comes back with (MISSING). This was tested apart from **fresh** and it works correctly with **go run**
```
func test() {
	v := url.Values{}
	v.Set("email", "test@test.com")
	log.Println(v.Encode())
}
```

Response using fresh:
`email=test%!t(MISSING)est.com`

Intended Response:
`email=test%40test.com`