DefaultFlow.java

import org.checkerframework.checker.nullness.qual.*;

@org.checkerframework.framework.qual.DefaultQualifier(NonNull.class)
public class DefaultFlow {

    void test() {

        @Nullable String reader = null;
        if (reader == null) {
            return;
        }

        reader.startsWith("hello");
    }

    void tesVariableInitialization() {
        @Nullable Object elts = null;
        assert elts != null : "@AssumeAssertion(nullness)";
        @NonNull Object elem = elts;
    }
}