A DESCRIPTION OF THE PROBLEM :
The preview pattern matching compiler feature in JDK 17 is not correctly recognizing that a variable is initialized unless a default case is added (which completely defeats the purpose of using the new switch statements). See the provided source code for more details.

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Attempt to compile the sample code using the '--enable-preview' option

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
The code should compile without errors.
ACTUAL -
javac -source 17 --enable-preview Example.java
Sample.java:18: error: variable description might not have been initialized
        return description;
               ^
Note: Sample.java uses preview features of Java SE 17.
Note: Recompile with -Xlint:preview for details.
1 error

---------- BEGIN SOURCE ----------
class Example
{
    sealed interface MyBoolean
    {
        record True() implements MyBoolean {}
        record False() implements MyBoolean {}
    }

    String describe(MyBoolean value)
    {
        final String description;

        switch (value) {
            case MyBoolean.True t -> description = "It's True";
            case MyBoolean.False f -> description = "It's False";
            //default -> throw new IllegalStateException("Cannot happen javac!");
        }

        return description;
    }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
You either must include a default statement or initialize the variable to some value (making it non-final), neither of which are acceptable.