Invalid mock-up for internal class

[ctlove0523]

I checked issue 326,but found not help me.

jmockit version：1.28

What confuse me is the mocked class is not a internal class, the below is my code:

public class CipherUtil {
    private static final HCCipherUtil CIPHER = new B();

    public static String encrypt(String plaintText) {
        return CIPHER.encrypt(plaintText);
    }

    public static String decrypt(String cipherText) {
        return CIPHER.decrypt(cipherText);
    }
}

I use the below code to mock:

new MockUp<CipherUtil>() {
    @Mock
    public String encrypt(String plaintText) {
        return plaintText;
    }

    @Mock
    public String decrypt(String cipherText) {
        return cipherText;
    }
};

it's works well but i get warning message: Invalid mock-up for internal class CipherUtil class.