【BUG?】Spring1 Spring2 Spring3 Invalid payload type 'null'

[winezer0]

java -jar ysoserial-for-woodpecker-0.5.2.jar Spring2 calc
java.lang.ClassNotFoundException: me.gv7.woodpecker.yso.payloads.null
at java.net.URLClassLoader.findClass(URLClassLoader.java:382)
at java.lang.ClassLoader.loadClass(ClassLoader.java:418)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355)
at java.lang.ClassLoader.loadClass(ClassLoader.java:351)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:264)
at me.gv7.woodpecker.yso.payloads.ObjectPayload$Utils.getPayloadClass(ObjectPayload.java:56)
at me.gv7.woodpecker.yso.GeneratePayload.main(GeneratePayload.java:55)
Invalid payload type 'null'