refactor: Annotate methods which may return null with @Nullable (#615)

Use this link to re-run the recipe: https://app.moderne.io/recipes/org.openrewrite.staticanalysis.AnnotateNullableMethods?organizationId=T3BlblJld3JpdGU%3D

Co-authored-by: Moderne <team@moderne.io>

Author: nielsdebruin

src/main/java/org/openrewrite/kotlin/KotlinVisitor.java

@@ -411,7 +411,7 @@ public <J2 extends J> JContainer<J2> visitContainer(JContainer<J2> container, P
         return super.visitContainer(container, JContainer.Location.LANGUAGE_EXTENSION, p);
     }
 
-    public <J2 extends J> JContainer<J2> visitContainer(@Nullable JContainer<J2> container,
+    public <J2 extends J> @Nullable JContainer<J2> visitContainer(@Nullable JContainer<J2> container,
                                                         KContainer.Location loc, P p) {
         if (container == null) {
             //noinspection ConstantConditions
@@ -429,7 +429,7 @@ public <J2 extends J> JContainer<J2> visitContainer(@Nullable JContainer<J2> con
                 JContainer.build(before, js, container.getMarkers());
     }
 
-    public <T> JLeftPadded<T> visitLeftPadded(@Nullable JLeftPadded<T> left, KLeftPadded.Location loc, P p) {
+    public <T> @Nullable JLeftPadded<T> visitLeftPadded(@Nullable JLeftPadded<T> left, KLeftPadded.Location loc, P p) {
         if (left == null) {
             //noinspection ConstantConditions
             return null;
@@ -458,7 +458,7 @@ public <T> JLeftPadded<T> visitLeftPadded(@Nullable JLeftPadded<T> left, KLeftPa
         return (before == left.getBefore() && t == left.getElement()) ? left : new JLeftPadded<>(before, t, left.getMarkers());
     }
 
-    public <T> JRightPadded<T> visitRightPadded(@Nullable JRightPadded<T> right, KRightPadded.Location loc, P p) {
+    public <T> @Nullable JRightPadded<T> visitRightPadded(@Nullable JRightPadded<T> right, KRightPadded.Location loc, P p) {
         if (right == null) {
             //noinspection ConstantConditions
             return null;

src/main/java/org/openrewrite/kotlin/format/TabsAndIndentsVisitor.java

@@ -248,7 +248,7 @@ public <T> JLeftPadded<T> visitLeftPadded(@Nullable JLeftPadded<T> left, JLeftPa
     }
 
     @Override
-    public <T> JRightPadded<T> visitRightPadded(@Nullable JRightPadded<T> right, JRightPadded.Location loc, P p) {
+    public <T> @Nullable JRightPadded<T> visitRightPadded(@Nullable JRightPadded<T> right, JRightPadded.Location loc, P p) {
         if (right == null) {
             //noinspection ConstantConditions
             return null;

src/main/java/org/openrewrite/kotlin/internal/PsiTreePrinter.java

@@ -123,16 +123,17 @@ public static class TreePrinterContext {
         int depth;
     }
 
-    public static String printFirFile(FirFile file) {
+    public static @Nullable String printFirFile(FirFile file) {
         StringBuilder sb = new StringBuilder();
         List<StringBuilder> lines = new ArrayList<>();
         sb.append("------------").append("\n");
         sb.append("FirFile:").append("\n\n");
 
         TreePrinterContext context = new TreePrinterContext(lines, 1);
         new FirDefaultVisitor<Void, TreePrinterContext>() {
+
             @Override
-            public Void visitElement(FirElement firElement, TreePrinterContext ctx) {
+            public @Nullable Void visitElement(FirElement firElement, TreePrinterContext ctx) {
                 StringBuilder line = new StringBuilder();
                 line.append(leftPadding(ctx.getDepth()))
                         .append(printFirElement(firElement));
@@ -153,17 +154,18 @@ public Void visitElement(FirElement firElement, TreePrinterContext ctx) {
                 return null;
             }
         }.visitFile(file, context);
-        sb.append(java.lang.String.join("\n", lines));
+        sb.append(String.join("\n", lines));
         return sb.toString();
     }
 
-    public static String printFirTree(FirElement firElement) {
+    public static @Nullable String printFirTree(FirElement firElement) {
         StringBuilder sb = new StringBuilder();
         List<StringBuilder> lines = new ArrayList<>();
         TreePrinterContext context = new TreePrinterContext(lines, 1);
         new FirDefaultVisitor<Void, TreePrinterContext>() {
+
             @Override
-            public Void visitElement(FirElement fir, TreePrinterContext ctx) {
+            public @Nullable Void visitElement(FirElement fir, TreePrinterContext ctx) {
                 StringBuilder line = new StringBuilder();
                 line.append(leftPadding(ctx.getDepth()))
                         .append(printFirElement(fir));
@@ -184,7 +186,7 @@ public Void visitElement(FirElement fir, TreePrinterContext ctx) {
                 return null;
             }
         }.visitElement(firElement, context);
-        sb.append(java.lang.String.join("\n", lines));
+        sb.append(String.join("\n", lines));
         return sb.toString();
     }