Prevent EqualsAvoidsNull from rewriting aString.equals(null) into null.equals(aString)

Author: sambsnyd

src/main/java/org/openrewrite/staticanalysis/EqualsAvoidsNullVisitor.java

@@ -47,15 +47,16 @@ public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, P p)
         }
 
         if ((STRING_EQUALS.matches(m) || (!Boolean.TRUE.equals(style.getIgnoreEqualsIgnoreCase()) && STRING_EQUALS_IGNORE_CASE.matches(m))) &&
-                m.getArguments().get(0) instanceof J.Literal &&
-                !(m.getSelect() instanceof J.Literal)) {
+            m.getArguments().get(0) instanceof J.Literal &&
+            m.getArguments().get(0).getType() != JavaType.Primitive.Null &&
+            !(m.getSelect() instanceof J.Literal)) {
             Tree parent = getCursor().getParentTreeCursor().getValue();
             if (parent instanceof J.Binary) {
                 J.Binary binary = (J.Binary) parent;
                 if (binary.getOperator() == J.Binary.Type.And && binary.getLeft() instanceof J.Binary) {
                     J.Binary potentialNullCheck = (J.Binary) binary.getLeft();
                     if ((isNullLiteral(potentialNullCheck.getLeft()) && matchesSelect(potentialNullCheck.getRight(), m.getSelect())) ||
-                            (isNullLiteral(potentialNullCheck.getRight()) && matchesSelect(potentialNullCheck.getLeft(), m.getSelect()))) {
+                        (isNullLiteral(potentialNullCheck.getRight()) && matchesSelect(potentialNullCheck.getLeft(), m.getSelect()))) {
                         doAfterVisit(new RemoveUnnecessaryNullCheck<>(binary));
                     }
                 }

src/test/java/org/openrewrite/staticanalysis/EqualsAvoidsNullTest.java

@@ -84,4 +84,19 @@ public class A {
           )
         );
     }
+
+    @Test
+    void nullLiteral() {
+        rewriteRun(
+            //language=java
+            java("""
+              public class A {
+                    void foo(String s) {
+                        if(s.equals(null)) {
+                        }
+                    }
+                }
+              """)
+        );
+    }
 }