Surround with null check: fix incorrect check for 'in' expression

#KT-31749 Fixed

idea/src/org/jetbrains/kotlin/idea/quickfix/SurroundWithNullCheckFix.kt

@@ -25,6 +25,7 @@ import org.jetbrains.kotlin.diagnostics.Errors
 import org.jetbrains.kotlin.idea.KotlinBundle
 import org.jetbrains.kotlin.idea.caches.resolve.analyze
 import org.jetbrains.kotlin.idea.intentions.branchedTransformations.isStableSimpleExpression
+import org.jetbrains.kotlin.lexer.KtTokens
 import org.jetbrains.kotlin.psi.*
 import org.jetbrains.kotlin.psi.psiUtil.createSmartPointer
 import org.jetbrains.kotlin.psi.psiUtil.getLastParentOfTypeInRow
@@ -68,7 +69,7 @@ class SurroundWithNullCheckFix(
             val nullableExpression =
                 when (parent) {
                     is KtDotQualifiedExpression -> parent.receiverExpression
-                    is KtBinaryExpression -> parent.left
+                    is KtBinaryExpression -> if (parent.operationToken == KtTokens.IN_KEYWORD) parent.right else parent.left
                     is KtCallExpression -> parent.calleeExpression
                     else -> return null
                 } as? KtReferenceExpression ?: return null

idea/testData/quickfix/surroundWithNullCheck/in.kt

@@ -0,0 +1,4 @@
+// "Surround with null check" "true"
+fun test(a: String, b: List<String>?) {
+    a <caret>in b
+}

idea/testData/quickfix/surroundWithNullCheck/in.kt.after

@@ -0,0 +1,6 @@
+// "Surround with null check" "true"
+fun test(a: String, b: List<String>?) {
+    if (b != null) {
+        a in b
+    }
+}

idea/tests/org/jetbrains/kotlin/idea/quickfix/QuickFixTestGenerated.java

@@ -13161,6 +13161,11 @@ public class QuickFixTestGenerated extends AbstractQuickFixTest {
             runTest("idea/testData/quickfix/surroundWithNullCheck/expressionUnsafeCall.kt");
         }
 
+        @TestMetadata("in.kt")
+        public void testIn() throws Exception {
+            runTest("idea/testData/quickfix/surroundWithNullCheck/in.kt");
+        }
+
         @TestMetadata("infixUnsafeCall.kt")
         public void testInfixUnsafeCall() throws Exception {
             runTest("idea/testData/quickfix/surroundWithNullCheck/infixUnsafeCall.kt");