When2Switch: check if entry set is not empty

compiler/backend/src/org/jetbrains/jet/codegen/when/SwitchCodegenUtil.java

@@ -101,6 +101,10 @@ public class SwitchCodegenUtil {
             boolean isStatement,
             @NotNull ExpressionCodegen codegen
     ) {
+        if (!isThereEntriesButElse(expression)) {
+            return null;
+        }
+
         Type subjectType = codegen.expressionType(expression.getSubjectExpression());
         BindingContext bindingContext = codegen.getBindingContext();
 
@@ -121,6 +125,11 @@ public class SwitchCodegenUtil {
         return null;
     }
 
+    private static boolean isThereEntriesButElse(@NotNull JetWhenExpression expression) {
+        List<JetWhenEntry> entries = expression.getEntries();
+        return !entries.isEmpty() && (entries.size() > 1 || !entries.get(0).isElse());
+    }
+
     private static boolean isIntegralConstantsSwitch(
             @NotNull JetWhenExpression expression,
             @NotNull Type subjectType,