Unexpected error registering jar plugin

[ertanyildiz]

I developed a simple plugin, created a jar in a folder and copied the folder to the $PENTAHO_PATH/plugins folder. When I restart PDI it gives the following error:

2020/04/06 16:27:43 - General - ERROR (version 9.0.0.0-423, build 9.0.0.0-423 from 2020-01-31 04.53.04 by buildguy) : Unexpected error registering jar plugin file: file:///home/username/Documents/pentaho/plugins/folder-name/myjar-name.jar
2020/04/06 16:27:43 - General - ERROR (version 9.0.0.0-423, build 9.0.0.0-423 from 2020-01-31 04.53.04 by buildguy) : java.lang.NullPointerException
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.plugins.StepPluginType.extractID(StepPluginType.java:149)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.plugins.BasePluginType.handlePluginAnnotation(BasePluginType.java:750)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.plugins.BasePluginType.registerPluginJars(BasePluginType.java:718)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.plugins.BasePluginType.searchPlugins(BasePluginType.java:184)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.plugins.PluginRegistry.registerType(PluginRegistry.java:605)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.plugins.PluginRegistry.init(PluginRegistry.java:577)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.plugins.PluginRegistry.init(PluginRegistry.java:545)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.KettleEnvironment.init(KettleEnvironment.java:145)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.KettleEnvironment.init(KettleEnvironment.java:100)
2020/04/06 16:27:43 - General -         at org.pentaho.di.core.KettleEnvironment.init(KettleEnvironment.java:81)
2020/04/06 16:27:43 - General -         at org.pentaho.di.ui.spoon.Spoon$1.call(Spoon.java:643)
2020/04/06 16:27:43 - General -         at org.pentaho.di.ui.spoon.Spoon$1.call(Spoon.java:635)
2020/04/06 16:27:43 - General -         at java.util.concurrent.FutureTask.run(FutureTask.java:266)
2020/04/06 16:27:43 - General -         at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
2020/04/06 16:27:43 - General -         at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
2020/04/06 16:27:43 - General -         at java.lang.Thread.run(Thread.java:748)

Do you have any idea why Pentaho does not build my plugin? Thank you.