Do not suggest replacing comparison to null with function call

So #KT-20620 Fixed

idea/idea-analysis/src/org/jetbrains/kotlin/idea/intentions/OperatorToFunctionIntention.kt

@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.idea.intentions
 
 import com.intellij.openapi.editor.Editor
 import com.intellij.psi.PsiElement
+import org.jetbrains.kotlin.KtNodeTypes
 import org.jetbrains.kotlin.config.LanguageFeature
 import org.jetbrains.kotlin.descriptors.FunctionDescriptor
 import org.jetbrains.kotlin.idea.caches.resolve.analyze
@@ -58,7 +59,8 @@ class OperatorToFunctionIntention : SelfTargetingIntention<KtExpression>(KtExpre
             val opRef = element.operationReference
             if (!opRef.textRange.containsOffset(caretOffset)) return false
             return when (opRef.getReferencedNameElementType()) {
-                KtTokens.PLUS, KtTokens.MINUS, KtTokens.MUL, KtTokens.DIV, KtTokens.PERC, KtTokens.RANGE, KtTokens.IN_KEYWORD, KtTokens.NOT_IN, KtTokens.PLUSEQ, KtTokens.MINUSEQ, KtTokens.MULTEQ, KtTokens.DIVEQ, KtTokens.PERCEQ, KtTokens.EQEQ, KtTokens.EXCLEQ, KtTokens.GT, KtTokens.LT, KtTokens.GTEQ, KtTokens.LTEQ -> true
+                KtTokens.PLUS, KtTokens.MINUS, KtTokens.MUL, KtTokens.DIV, KtTokens.PERC, KtTokens.RANGE, KtTokens.IN_KEYWORD, KtTokens.NOT_IN, KtTokens.PLUSEQ, KtTokens.MINUSEQ, KtTokens.MULTEQ, KtTokens.DIVEQ, KtTokens.PERCEQ, KtTokens.GT, KtTokens.LT, KtTokens.GTEQ, KtTokens.LTEQ -> true
+                KtTokens.EQEQ, KtTokens.EXCLEQ -> listOf(element.left, element.right).none { it?.node?.elementType == KtNodeTypes.NULL }
                 KtTokens.EQ -> element.left is KtArrayAccessExpression
                 else -> false
             }

idea/testData/intentions/operatorToFunction/binaryEqEqNotNullInLeftSide.kt

@@ -0,0 +1,6 @@
+// IS_APPLICABLE: false
+fun test(x: String?) {
+    if (null <caret>!= x) {
+        x.length
+    }
+}

idea/testData/intentions/operatorToFunction/binaryEqEqNotNullInRightSide.kt

@@ -0,0 +1,6 @@
+// IS_APPLICABLE: false
+fun test(x: String?) {
+    if (x <caret>!= null) {
+        x.length
+    }
+}

idea/testData/intentions/operatorToFunction/binaryEqEqNullInLeftSide.kt

@@ -0,0 +1,4 @@
+// IS_APPLICABLE: false
+fun test(x: String?) {
+    null <caret>== x
+}

idea/testData/intentions/operatorToFunction/binaryEqEqNullInRightSide.kt

@@ -0,0 +1,4 @@
+// IS_APPLICABLE: false
+fun test(x: String?) {
+    x <caret>== null
+}

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

@@ -11807,6 +11807,30 @@ public class IntentionTestGenerated extends AbstractIntentionTest {
             doTest(fileName);
         }
 
+        @TestMetadata("binaryEqEqNotNullInLeftSide.kt")
+        public void testBinaryEqEqNotNullInLeftSide() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/operatorToFunction/binaryEqEqNotNullInLeftSide.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("binaryEqEqNotNullInRightSide.kt")
+        public void testBinaryEqEqNotNullInRightSide() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/operatorToFunction/binaryEqEqNotNullInRightSide.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("binaryEqEqNullInLeftSide.kt")
+        public void testBinaryEqEqNullInLeftSide() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/operatorToFunction/binaryEqEqNullInLeftSide.kt");
+            doTest(fileName);
+        }
+
+        @TestMetadata("binaryEqEqNullInRightSide.kt")
+        public void testBinaryEqEqNullInRightSide() throws Exception {
+            String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/operatorToFunction/binaryEqEqNullInRightSide.kt");
+            doTest(fileName);
+        }
+
         @TestMetadata("binaryEqEqNullable.kt")
         public void testBinaryEqEqNullable() throws Exception {
             String fileName = KotlinTestUtils.navigationMetadata("idea/testData/intentions/operatorToFunction/binaryEqEqNullable.kt");