[kotlin] Prevent adding safe let call to the null constant

Added a check whether the nullable argument is the null constant to
avoid proposing the fix resulting in the unreachable code like
`f(null)` →  `null?.let { f(it) }`

^KTIJ-20993 Fixed

(cherry-picked from commit 22819bcce03e5d53687cd832375486635ffc1647)

IJ-MR-20704

GitOrigin-RevId: 7932bc25ab2cfa4647c2b1dd046412ae419d92ad

plugins/kotlin/idea/src/org/jetbrains/kotlin/idea/quickfix/WrapWithSafeLetCallFix.kt

@@ -114,8 +114,7 @@ class WrapWithSafeLetCallFix(
                 else -> return null
             }
 
-            if (!isNullabilityMismatch(expected = expectedType, actual = actualType)) return null
-
+            if (element.isNull() || !isNullabilityMismatch(expected = expectedType, actual = actualType)) return null
             return WrapWithSafeLetCallFix(call.getLastParentOfTypeInRow<KtQualifiedExpression>() ?: call, element)
         }
     }

plugins/kotlin/idea/tests/test/org/jetbrains/kotlin/idea/quickfix/QuickFixMultiFileTestGenerated.java

@@ -2293,6 +2293,11 @@ public abstract class QuickFixMultiFileTestGenerated extends AbstractQuickFixMul
             runTest("testData/quickfix/wrapWithSafeLetCall/javaNullabilityMismatchArgument2.test");
         }
 
+        @TestMetadata("javaNullabilityMismatchDoNotWrapNull.test")
+        public void testJavaNullabilityMismatchDoNotWrapNull() throws Exception {
+            runTest("testData/quickfix/wrapWithSafeLetCall/javaNullabilityMismatchDoNotWrapNull.test");
+        }
+
         @TestMetadata("javaReceiverNullabilityInvoke.test")
         public void testJavaReceiverNullabilityInvoke() throws Exception {
             runTest("testData/quickfix/wrapWithSafeLetCall/javaReceiverNullabilityInvoke.test");

plugins/kotlin/idea/tests/testData/quickfix/wrapWithSafeLetCall/javaNullabilityMismatchDoNotWrapNull.test

@@ -0,0 +1,51 @@
+// FILE: test.before.kt
+// "Wrap with '?.let { ... }' call" "false"
+// ACTION: Add 'toString()' call
+// ACTION: Add names in comment to call arguments
+// ACTION: Convert to run
+// ACTION: Convert to with
+// ACTION: Do not show hints for current method
+package p;
+
+fun test(x: Foo) {
+    x.foo(<caret>null);
+}
+
+// FILE: org/jspecify/nullness/NullMarked.java
+package org.jspecify.nullness;
+
+import static java.lang.annotation.ElementType.MODULE;
+import static java.lang.annotation.ElementType.PACKAGE;
+import static java.lang.annotation.ElementType.TYPE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+@Target({TYPE, PACKAGE, MODULE})
+@Retention(RUNTIME)
+public @interface NullMarked {}
+
+// FILE: org/jspecify/nullness/Nullable.java
+package org.jspecify.nullness;
+
+import static java.lang.annotation.ElementType.TYPE_USE;
+import static java.lang.annotation.RetentionPolicy.RUNTIME;
+
+import java.lang.annotation.Retention;
+import java.lang.annotation.Target;
+
+@Target(TYPE_USE)
+@Retention(RUNTIME)
+public @interface Nullable {}
+
+// FILE: p/Foo.java
+package p;
+
+import org.jspecify.nullness.NullMarked;
+
+@NullMarked
+public class Foo {
+    public void foo(String arg) {}
+}