Try passing null again, sign tests are failing on travis
Try passing null again, sign tests are failing on travis

afk11/secp256k1-php,afk11/secp256k1-php,Bit-Wasp/secp256k1-php,Bit-Wasp/secp256k1-php,Bit-Wasp/secp256k1-php,afk11/secp256k1-php,afk11/secp256k1-php,Bit-Wasp/secp256k1-php,afk11/secp256k1-php,Bit-Wasp/secp256k1-php