Surprising behavior of @NullUnmarked on method overriding Map.get()

[msridhar]

Test case:

NullAway/nullaway/src/test/java/com/uber/nullaway/NullAwayJSpecifyTests.java

Lines 1138 to 1151 in 5d9fbe1

	"TestMap.java",
	"package com.uber;",
	"import org.jspecify.annotations.NullUnmarked;",
	"public class TestMap extends java.util.HashMap<String,Object> {",
	" @NullUnmarked",
	" @Override",
	" public Object get(Object key) {",
	" return super.get(key);",
	" }",
	" public String getString(String key) {",
	" // should be no error here",
	" return (String) get(key);",
	" }",
	"}")

A user may expect that annotating the TestMap.get() method as @NullUnmarked would lead to its return being treated as @NonNull. But, our rules dictate that for unannotated code, inherited library models should apply. So, the inherited library model for Map.get() is applied, and the return becomes @Nullable. Not sure whether we need to fix something here, or whether this is unusual but sensible behavior. My intuition is that an explicit @NullUnmarked annotation should "win" over an inherited library method, but that will just make the rules even more complicated...