You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: none.go
    path of file: ./repos/teller/vendor/github.com/form3tech-oss/jwt-go
    
    the code of the file until where you have to start completion: package jwt

// Implements the none signing method.  This is required by the spec
// but you probab
    
func (m *signingMethodNone) Verify(signingString, signature string, key interface{}) (err error) {
	// Key must be UnsafeAllowNoneSignatureType to prevent accidentally
	// accepting 'none' signing method
	if _, ok := key.(unsafeNoneMagicConstant); !ok {
		return NoneSignatureTypeDisallowedError
	}
	// If signing method is none, signature must be an empty string
	if signature != "" {
		return NewValidationError(
			"'none' signing method with non-empty signature",
			ValidationErrorSignatureInvalid,
		)
	}

	// Accept 'none' signing method.
	return nil
}