Message11100

I have been having a look at this issue as I am also seeing this. But I think it is OS dependent. It seems to work ok on RHEL6 but it is failing on Ubuntu 16.04 64 bit.

Jython 2.7.1b3 (, Feb 19 2017, 19:57:56) 
[Java HotSpot(TM) 64-Bit Server VM (Oracle Corporation)] on java1.8.0_121
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>>> import os
>>> os.getlogin()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
	at org.python.core.PyString.<init>(PyString.java:62)
	at org.python.core.PyString.<init>(PyString.java:70)
	at org.python.modules.posix.PosixModule.getlogin(PosixModule.java:528)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:498)

java.lang.IllegalArgumentException: java.lang.IllegalArgumentException: Cannot create PyString from null
>>> 

I was running a just built version of jython master.

Could you provide some more details of the OS and java you were using.