diff --git a/src/main/java/com/google/api/generator/engine/ast/ClassDefinition.java b/src/main/java/com/google/api/generator/engine/ast/ClassDefinition.java
index 76c797c7d3..ec8f4f7b43 100644
--- a/src/main/java/com/google/api/generator/engine/ast/ClassDefinition.java
+++ b/src/main/java/com/google/api/generator/engine/ast/ClassDefinition.java
@@ -137,6 +137,7 @@ public ClassDefinition build() {
       setClassIdentifier(classIdentifier);
 
       ClassDefinition classDef = autoBuild();
+      performNullChecks(classDef);
 
       // Only nested classes can forego having a package.
       if (!classDef.isNested()) {
@@ -201,5 +202,19 @@ public ClassDefinition build() {
 
       return classDef;
     }
+
+    void performNullChecks(ClassDefinition classDef) {
+      String contextInfo = String.format("class  definition of %s", name());
+      NodeValidator.checkNoNullElements(
+          classDef.headerCommentStatements(), "header comments", contextInfo);
+      NodeValidator.checkNoNullElements(classDef.annotations(), "annotations", contextInfo);
+
+      NodeValidator.checkNoNullElements(
+          classDef.implementsTypes(), "implemented types", contextInfo);
+      NodeValidator.checkNoNullElements(classDef.statements(), "statements", contextInfo);
+
+      NodeValidator.checkNoNullElements(classDef.methods(), "methods", contextInfo);
+      NodeValidator.checkNoNullElements(classDef.nestedClasses(), "nested classes", contextInfo);
+    }
   }
 }