Unexpected error on cancelling [ Change ClassFile Versions] plugin window

[greenozon]

Steps to reproduce

1. open up any jar

2. go to Plugins -> Change ClassFile Versions menu item
   it'll show this window:
   

3. press Cancel button

it'll print out some exception:

Please send this error log to https://github.com/Konloch/bytecode-viewer/issues or Konloch at https://the.bytecode.club or konloch@gmail.com
If you hold appropriate legal rights to the relevant class/jar/apk file please include that as well.
Bytecode Viewer Version: 2.11.2 [Fat Jar], OS: Windows 7, Java: 1.8.0_331

java.lang.NumberFormatException: null
	at java.lang.Integer.parseInt(Integer.java:542)
	at java.lang.Integer.parseInt(Integer.java:615)
	at the.bytecode.club.bytecodeviewer.plugin.preinstalled.ChangeClassFileVersions.execute(ChangeClassFileVersions.java:25)
	at the.bytecode.club.bytecodeviewer.api.Plugin.lambda$executeContainer$0(Plugin.java:88)
	at java.util.LinkedHashMap$LinkedValues.forEach(LinkedHashMap.java:608)
	at the.bytecode.club.bytecodeviewer.api.Plugin.executeContainer(Plugin.java:83)
	at the.bytecode.club.bytecodeviewer.api.Plugin.run(Plugin.java:49)

Expectation: no exception at all