This test produces 3 unexpected type errors:

    static class Outer {
        class Inner<T> implements Runnable { public void run() {} }
    }

    void test(Outer outer) {
        Outer.Inner<String> inner1 = outer.new Inner<>(); // ok
        Outer.Inner<String> inner2 = test ? outer.new Inner<>() : null; // error
        Outer.Inner<String> inner3 = test ? null: outer.new Inner<>(); // error
        Outer.Inner<String> inner4 = test ? outer.new Inner<String>() : outer.new Inner<>(); // error
    }
    
The conditional expressions are treated as standalone, despite appearing in an assignment context. So the diamond instance creation always infers Inner<Object>, not Inner<String>.

Some initial testing seems to trace the issue to a false positive coming from Attr.isBooleanOrNumeric.