FormatterException on combined `null, default` switch expression branch

Hi team, case null, default -> is a common pattern in switch expressions (explicit null is required for compatibility with older switch statements). But it crashes the formatter, e.g. the code below results in /YourFile.java: com.palantir.javaformat.java.FormatterException: 48:13: error: expected token: 'default'; generated - instead -> [Help 1]

public void onReceive(Object message) {
    switch (message) {
        //...
        case null, default -> super.unhandled(message);
    }
}

Splitting the case into two separated cases with identical bodies helps, but it's obviously a subpar workaround because it causes static analyzer warnings + prevents switching to palantir-java-formatter without migrating all affected switches in the codebase first.

Thanks !

Start by reproducing the formatter failure with the provided Java switch-expression example and trace how combined null, default case labels are parsed. Done means the formatter accepts this syntax without raising FormatterException and preserves the intended switch expression formatting; add or update a regression test where the project's existing formatter tests cover this behavior.