diff --git a/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadProcessor.java b/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadProcessor.java
index 8914c9a..437fc45 100644
--- a/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadProcessor.java
+++ b/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadProcessor.java
@@ -3,6 +3,7 @@
 import com.google.auto.service.AutoService;
 import com.sun.tools.javac.api.JavacTrees;
 import com.sun.tools.javac.processing.JavacProcessingEnvironment;
+import com.sun.tools.javac.tree.JCTree;
 import com.sun.tools.javac.tree.TreeMaker;
 import com.sun.tools.javac.util.Context;
 import com.sun.tools.javac.util.Names;
@@ -38,7 +39,12 @@ public synchronized void init(ProcessingEnvironment processingEnv) {
     @Override
     public boolean process(Set<? extends TypeElement> annotations, RoundEnvironment roundEnv) {
         MethodOverloadTranslator visitor = new MethodOverloadTranslator(treeMaker, messager, names);
-        roundEnv.getRootElements().forEach(element -> trees.getTree(element).accept(visitor));
+        roundEnv.getRootElements().forEach(element -> {
+            JCTree tree = trees.getTree(element);
+            if (tree != null) {
+                tree.accept(visitor);
+            }
+        });
         return true;
     }
 }
\ No newline at end of file
diff --git a/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadTranslator.java b/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadTranslator.java
index 76bb198..4f2f3c0 100644
--- a/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadTranslator.java
+++ b/nusadua/src/main/java/io/github/leibnizhu/nusadua/MethodOverloadTranslator.java
@@ -43,7 +43,7 @@ public MethodOverloadTranslator(TreeMaker treeMaker, Messager messager, Names na
      */
     @Override
     public void visitClassDef(JCTree.JCClassDecl jcClass) {
-        String classFullName = jcClass.sym.fullname.toString();
+        String classFullName = Optional.ofNullable(jcClass.sym).map(s -> s.fullname).map(Object::toString).orElse("");
         Queue<JCTree.JCMethodDecl> newMethods = new LinkedList<>();
         Map<String, Set<String>> methodSignMap = new HashMap<>(); //Map<MethodName, Set<ParameterTypeList>>
         jcClass.defs.stream()