KT-13884 Exception "Invalid root block PSI element" on replacing trivial when-expression to if

#KT-13884 Fixed

idea/src/org/jetbrains/kotlin/idea/intentions/branchedTransformations/intentions/WhenToIfIntention.kt

@@ -33,6 +33,7 @@ class WhenToIfIntention : SelfTargetingRangeIntention<KtWhenExpression>(KtWhenEx
         if (entries.isEmpty()) return null
         val lastEntry = entries.last()
         if (entries.any { it != lastEntry && it.isElse }) return null
+        if (entries.all { it.isElse }) return null // 'when' with only 'else' branch is not supported
         return element.whenKeyword.textRange
     }
 

idea/testData/intentions/branched/ifWhen/whenToIf/kt13884.kt

@@ -0,0 +1,6 @@
+//IS_APPLICABLE: false
+fun foo() {
+    <caret>when {
+        else -> {}
+    }
+}

idea/tests/org/jetbrains/kotlin/idea/intentions/IntentionTestGenerated.java

@@ -1771,6 +1771,12 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("kt13884.kt")
+                public void testKt13884() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/branched/ifWhen/whenToIf/kt13884.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("whenWithDotQualifiedExpression.kt")
                 public void testWhenWithDotQualifiedExpression() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/branched/ifWhen/whenToIf/whenWithDotQualifiedExpression.kt");