Added regression tests for KT-3518 Null pointer during null comparison in JS Backend.

js/js.tests/test/org/jetbrains/k2js/test/semantics/EqualsTest.java

@@ -49,4 +49,8 @@ public final class EqualsTest extends AbstractExpressionTest {
     public void testEqualsNullOrUndefined() throws Exception {
         checkFooBoxIsOk();
     }
+
+    public void testCompareNullableListWithNull() throws Exception {
+        checkFooBoxIsOk();
+    }
 }

js/js.translator/testData/expression/equals/cases/compareNullableListWithNull.kt

@@ -0,0 +1,14 @@
+// KT-3518 Null pointer during null comparison in JS Backend
+package foo
+
+class MyClazz(val nullableL : List<String>?)
+
+fun box(): String {
+    val a = MyClazz(null)
+    if(a.nullableL != null) return "a.nullableL != null"
+
+    val b = MyClazz(listOf("somthing"))
+    if(b.nullableL == null) return "b.nullableL == null"
+
+    return "OK"
+}