A DESCRIPTION OF THE PROBLEM :
Trying to use a pattern in a switch statement (as outlined in JEP 406) when switching on `null` results in a compile-time assertion error, "java.lang.AssertionError: unexpected type: <nulltype>"

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Compile the provided source code with

javac Bug.java --enable-preview --release 17

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
javac should exit successfully without error after having compiled the file
ACTUAL -
Note: Bug.java uses preview features of Java SE 17.
Note: Recompile with -Xlint:preview for details.
An exception has occurred in the compiler (17-ea). Please file a bug against the Java compiler via the Java bug reporting page (http://bugreport.java.com) after checking the Bug Database (http://bugs.java.com) for duplicates. Include your program, the following diagnostic, and the parameters passed to the Java compiler in your report. Thank you.
java.lang.AssertionError: unexpected type: <nulltype>
        at jdk.compiler/com.sun.tools.javac.tree.TreeMaker.Type(TreeMaker.java:860)
        at jdk.compiler/com.sun.tools.javac.tree.TreeMaker.VarDef(TreeMaker.java:882)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.handleSwitch(TransPatterns.java:384)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.visitSwitch(TransPatterns.java:259)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCSwitch.accept(JCTree.java:1294)
        at jdk.compiler/com.sun.tools.javac.tree.TreeTranslator.translate(TreeTranslator.java:58)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.visitBlock(TransPatterns.java:685)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCBlock.accept(JCTree.java:1091)
        at jdk.compiler/com.sun.tools.javac.tree.TreeTranslator.translate(TreeTranslator.java:58)
        at jdk.compiler/com.sun.tools.javac.tree.TreeTranslator.visitMethodDef(TreeTranslator.java:150)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.visitMethodDef(TransPatterns.java:632)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCMethodDecl.accept(JCTree.java:921)
        at jdk.compiler/com.sun.tools.javac.tree.TreeTranslator.translate(TreeTranslator.java:58)
        at jdk.compiler/com.sun.tools.javac.tree.TreeTranslator.translate(TreeTranslator.java:70)
        at jdk.compiler/com.sun.tools.javac.tree.TreeTranslator.visitClassDef(TreeTranslator.java:139)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.visitClassDef(TransPatterns.java:712)
        at jdk.compiler/com.sun.tools.javac.tree.JCTree$JCClassDecl.accept(JCTree.java:819)
        at jdk.compiler/com.sun.tools.javac.tree.TreeTranslator.translate(TreeTranslator.java:58)
        at jdk.compiler/com.sun.tools.javac.comp.TransPatterns.translateTopLevelClass(TransPatterns.java:741)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.desugar(JavaCompiler.java:1535)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.desugar(JavaCompiler.java:1408)
        at jdk.compiler/com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:946)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:317)
        at jdk.compiler/com.sun.tools.javac.main.Main.compile(Main.java:176)
        at jdk.compiler/com.sun.tools.javac.Main.compile(Main.java:64)
        at jdk.compiler/com.sun.tools.javac.Main.main(Main.java:50)
printing javac parameters to: C:\Users\user\Java\foo\javac.20210708_191807.args

---------- BEGIN SOURCE ----------
class Bug {
    public static void main(String[] args) {
        switch (null) {
            case Integer i: return;
        }
    }
}
---------- END SOURCE ----------

FREQUENCY : always