Another CFG construction crash when both cases of a ConditionalExpression are the null literal

[msridhar]

Following up to #6743 I am still seeing a crash during CFG construction but with a slightly different test input:

public class Crash {
  String foo2(String x) { return x.isEmpty() ? null : null; }
}

Sorry I should have tested out the previous fix earlier; I just got to testing it with the 3.47.0 release. An input like the above still crashes NullAway.

[msridhar]

Thanks for the fix! I confirmed the NullAway crash no longer appears.