output: #fixed code
                                  @CheckForNull
      @Override
      public CNode describe(T instance) throws Exception {
  
          // Here we assume a correctly designed DataBound Object will have required attributes set by DataBoundConstructor
          // and all others using DataBoundSetters. So constructor parameters for sure are part of the description, others
          // need to be compared with default values.
  
          // Build same object with only constructor parameters
          final Constructor constructor = getDataBoundConstructor(target);
  
          final Parameter[] parameters = constructor.getParameters();
          final String[] names = ClassDescriptor.loadParameterNames(constructor);
          final Attribute[] attributes = new Attribute[parameters.length];
          final Object[] args = new Object[parameters.length];
          for (int i = 0; i < parameters.length; i++) {
              final Parameter p = parameters[i];
              final Attribute a = detectActualType(names[i], p.getParameterizedType());
              args[i] = a.getValue(instance);
              attributes[i] = a;
          }
  
          T ref = (T) constructor.newInstance(args);
  
          // compare instance with this "default" object
          Mapping mapping = compare(instance, ref);
  
          // add constructor parameters
          for (int i = 0; i < parameters.length; i++) {
              final Configurator c = Configurator.lookup(attributes[i].getType());
              if (args[i] == null) continue;
              mapping.put(names[i], attributes[i].describe(args[i]));
          }
  
          return mapping;
      }
input: #vulnerable code 
                                  @CheckForNull
      @Override
      public CNode describe(T instance) throws Exception {
  
          // Here we assume a correctly designed DataBound Object will have required attributes set by DataBoundConstructor
          // and all others using DataBoundSetters. So constructor parameters for sure are part of the description, others
          // need to be compared with default values.
  
          // Build same object with only constructor parameters
          final Constructor constructor = getDataBoundConstructor(target);
  
          final Parameter[] parameters = constructor.getParameters();
          final String[] names = ClassDescriptor.loadParameterNames(constructor);
          final Attribute[] attributes = new Attribute[parameters.length];
          final Object[] args = new Object[parameters.length];
          for (int i = 0; i < parameters.length; i++) {
              final Parameter p = parameters[i];
              final Attribute a = detectActualType(names[i], p.getParameterizedType());
              args[i] = a.getValue(instance);
              attributes[i] = a;
          }
  
          T ref = (T) constructor.newInstance(args);
  
          // compare instance with this "default" object
          Mapping mapping = compare(instance, ref);
  
          // add constructor parameters
          for (int i = 0; i < parameters.length; i++) {
              final Configurator c = Configurator.lookup(attributes[i].getType());
              mapping.put(names[i], c.describe(args[i]));
          }
  
          return mapping;
      } 
                              #location 31 
                              #vulnerability type NULL_DEREFERENCE