Proguard keeps string constants used for logging

Question

Following Removing unused strings during ProGuard optimisation I created Logg class that is designed to be easily removed by Proguard:

public class Logg {
    public static void e(Object... args) {
        Log.e(TAG, buildString(args));
    }

    public static void d(Object... args) {
        Log.d(TAG, buildString(args));
    }
}

Next, I added these rules to proguard-rules.pro used by project:

-assumenosideeffects class com.mypackage.Logg {
    public static *** d(...);
    public static *** e(...);
}
-optimizationpasses 10

After the project is built, I inspect the resulting classes.jar file with JD-GUI and see lines like these:

new Object[1][0] = "Some log message";

The Logg.e(... call is removed but the constant is still there. With -optimizationpasses 5 the line was mentioning String instead of Object.

Is there a way to make sure that Proguard will remove those Strings?