Replace aString.equals(null) with aString == null

Author: sambsnyd

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

@@ -19,36 +19,35 @@
 import lombok.Value;
 import org.openrewrite.Tree;
 import org.openrewrite.internal.lang.Nullable;
-import org.openrewrite.java.JavaIsoVisitor;
 import org.openrewrite.java.JavaVisitor;
 import org.openrewrite.java.MethodMatcher;
 import org.openrewrite.java.style.EqualsAvoidsNullStyle;
-import org.openrewrite.java.tree.Expression;
-import org.openrewrite.java.tree.J;
-import org.openrewrite.java.tree.JavaType;
-import org.openrewrite.java.tree.Space;
+import org.openrewrite.java.tree.*;
+import org.openrewrite.marker.Markers;
 
 import static java.util.Collections.singletonList;
 
 @Value
 @EqualsAndHashCode(callSuper = false)
-public class EqualsAvoidsNullVisitor<P> extends JavaIsoVisitor<P> {
+public class EqualsAvoidsNullVisitor<P> extends JavaVisitor<P> {
     private static final MethodMatcher STRING_EQUALS = new MethodMatcher("String equals(java.lang.Object)");
     private static final MethodMatcher STRING_EQUALS_IGNORE_CASE = new MethodMatcher("String equalsIgnoreCase(java.lang.String)");
 
     EqualsAvoidsNullStyle style;
 
     @Override
-    public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, P p) {
-        J.MethodInvocation m = super.visitMethodInvocation(method, p);
-
+    public J visitMethodInvocation(J.MethodInvocation method, P p) {
+        J j = super.visitMethodInvocation(method, p);
+        if (!(j instanceof J.MethodInvocation)) {
+            return j;
+        }
+        J.MethodInvocation m = (J.MethodInvocation) j;
         if (m.getSelect() == null) {
             return m;
         }
 
         if ((STRING_EQUALS.matches(m) || (!Boolean.TRUE.equals(style.getIgnoreEqualsIgnoreCase()) && STRING_EQUALS_IGNORE_CASE.matches(m))) &&
             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) {
@@ -62,8 +61,16 @@ public J.MethodInvocation visitMethodInvocation(J.MethodInvocation method, P p)
                 }
             }
 
-            m = m.withSelect(((J.Literal) m.getArguments().get(0)).withPrefix(m.getSelect().getPrefix()))
-                    .withArguments(singletonList(m.getSelect().withPrefix(Space.EMPTY)));
+            if (m.getArguments().get(0).getType() == JavaType.Primitive.Null) {
+                return new J.Binary(Tree.randomId(), m.getPrefix(), Markers.EMPTY,
+                        m.getSelect(),
+                        JLeftPadded.build(J.Binary.Type.Equal).withBefore(Space.SINGLE_SPACE),
+                        m.getArguments().get(0).withPrefix(Space.SINGLE_SPACE),
+                        JavaType.Primitive.Boolean);
+            } else {
+                m = m.withSelect(((J.Literal) m.getArguments().get(0)).withPrefix(m.getSelect().getPrefix()))
+                        .withArguments(singletonList(m.getSelect().withPrefix(Space.EMPTY)));
+            }
         }
 
         return m;

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

@@ -96,6 +96,15 @@ void foo(String s) {
                         }
                     }
                 }
+              """,
+              """
+
+              public class A {
+                    void foo(String s) {
+                        if(s == null) {
+                        }
+                    }
+                }
               """)
         );
     }