output: #fixed code
                                public static ClassName get(Class<?> clazz) {
      checkNotNull(clazz, "clazz == null");
      checkArgument(!clazz.isPrimitive(), "primitive types cannot be represented as a ClassName");
      checkArgument(!void.class.equals(clazz), "'void' type cannot be represented as a ClassName");
      checkArgument(!clazz.isArray(), "array types cannot be represented as a ClassName");
  
      String anonymousSuffix = "";
      while (clazz.isAnonymousClass()) {
        int lastDollar = clazz.getName().lastIndexOf('$');
        anonymousSuffix = clazz.getName().substring(lastDollar) + anonymousSuffix;
        clazz = clazz.getEnclosingClass();
      }
      String name = clazz.getSimpleName() + anonymousSuffix;
  
      if (clazz.getEnclosingClass() == null) {
        // Avoid unreliable Class.getPackage(). https://github.com/square/javapoet/issues/295
        int lastDot = clazz.getName().lastIndexOf('.');
        String packageName = (lastDot != -1) ? clazz.getName().substring(0, lastDot) : NO_PACKAGE;
        return new ClassName(packageName, null, name);
      }
  
      return ClassName.get(clazz.getEnclosingClass()).nestedClass(name);
    }
input: #vulnerable code 
                                public static ClassName get(Class<?> clazz) {
      checkNotNull(clazz, "clazz == null");
      checkArgument(!clazz.isPrimitive(), "primitive types cannot be represented as a ClassName");
      checkArgument(!void.class.equals(clazz), "'void' type cannot be represented as a ClassName");
      checkArgument(!clazz.isArray(), "array types cannot be represented as a ClassName");
  
      String anonymousSuffix = "";
      while (clazz.isAnonymousClass()) {
        int lastDollar = clazz.getName().lastIndexOf('$');
        anonymousSuffix = clazz.getName().substring(lastDollar) + anonymousSuffix;
        clazz = clazz.getEnclosingClass();
      }
      String name = clazz.getSimpleName() + anonymousSuffix;
  
      if (clazz.getEnclosingClass() == null) {
        // Avoid unreliable Class.getPackage(). https://github.com/square/javapoet/issues/295
        int lastDot = clazz.getName().lastIndexOf('.');
        String packageName = (lastDot != -1) ? clazz.getName().substring(0, lastDot) : null;
        return new ClassName(packageName, null, name);
      }
  
      return ClassName.get(clazz.getEnclosingClass()).nestedClass(name);
    } 
                              #location 19 
                              #vulnerability type NULL_DEREFERENCE