LdapExtLoginModule fails if no initial bind credentials are supplied but anonymous login would be possible

If an anonymous bind to the LDAP-Server is allowed no bindDN and bindCredential is supplied in login-context.xml. This causes the LoginModule to fail due to an NPE. The responsible lines are around 485:

env.setProperty(Context.SECURITY_PRINCIPAL, dn);
env.put(Context.SECURITY_CREDENTIALS, credential);

The HashMap.put fails if dn or credetials are null. The obvious solution is to change the lines to:

if (dn != null)
env.setProperty(Context.SECURITY_PRINCIPAL, dn);
if (credential != null)
env.put(Context.SECURITY_CREDENTIALS, credential);