Covariant annotations for Java 8 stream classes

I was trying to create a test case for someting similar to https://github.com/typetools/checker-framework/issues/886 when I got this:

A.java:10: warning: [argument.type.incompatible] incompatible types in argument.
        return t(sb, false);
                 ^
  found   : @Initialized @NonNull Supplier<@Initialized @NonNull Boolean>
  required: @Initialized @NonNull Supplier<@Initialized @Nullable Boolean>

Is this normal?

import java.util.function.Supplier;
import org.checkerframework.checker.nullness.qual.Nullable;

public class A {

    public boolean b(Supplier<Boolean> sb) {
        return t(sb, false);
    }

    public <T> T t(Supplier<@Nullable T> st, T ifNull) {
        T get = st.get();
        return get != null ? get : ifNull;
    }

}

Start by compiling the supplied A.java reproduction with the Checker Framework and inspect how Java 8 Supplier and stream-related annotations are declared. Determine the intended treatment of the Supplier argument and use the existing annotation tests, if located, to verify the expected result.