14.11.1: Missing condition to exclude null value as a valid case constant

The bug description below is inaccurate. A constant variable is a valid constant expression, but to be a constant variable, the variable's declaration must initialize the variable with a constant expression. `final String value = null;` does not, in fact, declare a constant variable, so the simple name `value` is not a constant expression and `case value -> ...` is not legal.

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The JLS does not include sufficient conditions in 14.11.1 to exclude the null value as a case constant.

JLS 14.11.1 states that "...null cannot be used as a case constant". This is enforced by requiring that the case constant is a constant expression, as the null literal is not a valid constant expression.

Whilst necessary, this is not a sufficient condition. A constant variable is a valid constant expression. So, the specification as it stands would permit the following:

String selector = "hello";
final String value = null;
switch (selector){
    case value -> System.out.println("oops");
}
 
[Note that the compiler correctly rejects this example.]

Before the refactoring of the JLS to handle switch expressions, there was the following additional check, which is missing in the current version:

    No case constant associated with the switch statement is null.

Suggested change: Replace

    Every case constant must be either a constant expression (§15.29) or the name of an enum constant (§8.9.1), or a compile-time error occurs.

with the following:

    Every case constant must be either a constant expression (§15.29) that is not null or the name of an enum constant (§8.9.1), or a compile-time error occurs.