After the change for disabling DES-related etypes, JAAS login fails at the test fails with NPE.
Test Configuration :
-------------------------
SEAM instance SEAM.THREE.COM was used
Client side krb5.conf has
     default_tkt_enctypes=des-cbc-md5
     default_tgs_enctypes=des-cbc-md5
     permitted_enctypes=des-cbc-md5
does not have allow_weak_crypto = true

At this point a meaningful error message
like "Failure unspecified at GSS-API level (Mechanism level: Encryption type DES CBC mode with CRC-32 is not supported/enabled)"
is expected.
Instead a NPE is obtained


javax.security.auth.login.LoginException: java.lang.NullPointerException
        at sun.security.krb5.internal.KDCReqBody.asn1Encode(KDCReqBody.java:251)
        at sun.security.krb5.internal.KDCReq.asn1Encode(KDCReq.java:203)
        at sun.security.krb5.KrbAsReq.encoding(KrbAsReq.java:145)
        at sun.security.krb5.KrbAsReqBuilder.send(KrbAsReqBuilder.java:316)
        at sun.security.krb5.KrbAsReqBuilder.action(KrbAsReqBuilder.java:361)
        at com.sun.security.auth.module.Krb5LoginModule.attemptAuthentication(Krb5LoginModule.java:765)
        at com.sun.security.auth.module.Krb5LoginModule.login(Krb5LoginModule.java:616)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:491)
        at javax.security.auth.login.LoginContext.invoke(LoginContext.java:777)
        at javax.security.auth.login.LoginContext.access$000(LoginContext.java:195)
        at javax.security.auth.login.LoginContext$4.run(LoginContext.java:690)
        at javax.security.auth.login.LoginContext$4.run(LoginContext.java:688)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.login.LoginContext.invokePriv(LoginContext.java:688)
        at javax.security.auth.login.LoginContext.login(LoginContext.java:586)
        at Server.main(Server.java:670)

If krb5.conf in the clientside is modified to include "allow_weak_crypto = true"
login happens