Compilation error thrown while doing a boxing conversion on selector expression

The below code should compile successfully.

class PatternTest {
    public static void main(String[] args) {

        int selExpr = 1;
        int retval = switch (selExpr) {
            case Integer p -> 6;
            default -> 1;
        };
        System.out.println(retval);
    }
}

However, the compilation throws error with JDK 18 b25:

jdk-18/bin/javac --enable-preview -source 18 PatternTest.java
PatternTest.java:6: error: bad operand type int for unary operator '<*nullchk*>'
        int retval = switch (selExpr) {
                            ^
Note: PatternTest.java uses preview features of Java SE 18.