Update Confluence Custom Plugin 5.7 to 7.1 from JAR file

[Pavan Asknani]

We have create one plugin in confluence 5.7 and now we want to update it to work with 7.1 

We are facing "Java.lang.NullPointerException" error in 7.1 , kindly let us know how we can update it from JAR file. (We don't have source code) 

Note: we are facing issue in opening our configuration page , there is no issue in uploading or enable plugin.

Thanks