Flow.java

import org.checkerframework.checker.initialization.qual.NotOnlyInitialized;
import org.checkerframework.checker.initialization.qual.UnknownInitialization;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;

public class Flow {

    @NonNull String f;
    @NotOnlyInitialized @NonNull String g;

    public Flow(String arg) {
        //:: error: (dereference.of.nullable)
        f.toLowerCase();
        //:: error: (dereference.of.nullable)
        g.toLowerCase();
        f = arg;
        g = arg;
        foo();
        f.toLowerCase();
        //:: error: (method.invocation.invalid)
        g.toLowerCase();
        f = arg;
    }

    void test() {
        @Nullable String s = null;
        s = "a";
        s.toLowerCase();
    }

    void test2(@Nullable String s) {
        if (s != null) {
            s.toLowerCase();
        }
    }

    void foo(@UnknownInitialization Flow this) {}

    // TODO Pure, etc.
}