Enum.values() throws NullPointerException if switch statement exists

Following class will compile but throws an error when calling the "values()" method on the enum class.
With source level 1.8 this works but source level > 1.8 will throw

```
Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: java.lang.NullPointerException: Cannot read the array length because "" is null
at test_bug/test.FooEnum.values(FooEnum.java:1)
at test_bug/test.Foo.$SWITCH_TABLE$test$FooEnum(FooEnum.java:15)
at test_bug/test.Foo.(FooEnum.java:15)
```

```
public enum FooEnum implements Foo {

A, B;

public static void main(String[] args) {
FooEnum.values();
System.out.println("Works");
}
}

interface Foo {

// random field breaks byte code
String RANDOM_STRING = "bar";

// unused switch
default String breaksCompilation(FooEnum enumValue) {
switch (enumValue) {
case A:
return "A";
default :
return "";
}
}
}
```
The error can only be reproduced as long as interface "Foo" contains a switch statement AND a field. If "RANDOM_STRING" or the switch statement is removed the error will disappear.

Tested with ECJ version 3.31