#vulnerable code 
                                public static Object callPluginMethod(Class pluginClass, ClassLoader appClassLoader, String method, Class[] paramTypes, Object[] params) {
        Object pluginInstance = PluginManager.getInstance().getPlugin(pluginClass.getName(), appClassLoader);

        try {
            Method m = pluginInstance.getClass().getDeclaredMethod(method, paramTypes);
            return m.invoke(pluginInstance, params);
        } catch (Exception e) {
            throw new Error(String.format("Exception calling method {} on plugin class {}", method, pluginClass), e);
        }
    } 
                            #location 5 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                                public static Object callPluginMethod(Class pluginClass, ClassLoader appClassLoader, String method, Class[] paramTypes, Object[] params) {
        Object pluginInstance = PluginManager.getInstance().getPlugin(pluginClass.getName(), appClassLoader);

        try {
            Method m = pluginInstance.getClass().getDeclaredMethod(method, paramTypes);
            return m.invoke(pluginInstance, params);
        } catch (Exception e) {
            throw new Error(String.format("Exception calling method %s on plugin class %s", method, pluginClass), e);
        }
    }