#1 Improve error handling for configuration errors

[Guido Leenders]

In web.xml I had placed:

<init-param>
<param-name>spnego.login.server.module</param-name>
<param-value>invantive-tomcat-spnego-server</param-value>
</init-param>

but made an error in the param-value. Result was:

SEVERE: Exception starting filter SpnegoHttpFilter
java.lang.NullPointerException
at net.sourceforge.spnego.SpnegoFilterConfig.doServerModule(SpnegoFilterConfig.java:226)
at net.sourceforge.spnego.SpnegoFilterConfig.<init>(SpnegoFilterConfig.java:141)
at net.sourceforge.spnego.SpnegoFilterConfig.getInstance(SpnegoFilterConfig.java:314)

Reason: the param-value does not exist in login.conf.

Current code in spnegofilter.config:

final AppConfigurationEntry entry = config.getAppConfigurationEntry(moduleName)[0];

suggestion: add an "if ... null" then raise message such as "Can not find module MODULENAME in THE VALUE OF LOGIN.conf

It had me puzzling for 15 minutes as a first-time user of spnego.