Initialization fails when providing an empty logback.configurationFile system property

[maartenc]

Hi,

when starting our application with an empty logback.configurationFile system property, the logback initialization fails.
It would be nice if this was handled more gracefully.

For instance, starting the application with -Dlogback.configurationFile= result in the following exception being logged:

Failed to instantiate [ch.qos.logback.classic.LoggerContext]
Reported exception:
ch.qos.logback.core.LogbackException: Failed to initialize or to run Configurator: ch.qos.logback.classic.util.DefaultJoranConfigurator
        at ch.qos.logback.classic.util.ContextInitializer.invokeConfigure(ContextInitializer.java:147)
        at ch.qos.logback.classic.util.ContextInitializer.autoConfig(ContextInitializer.java:101)
        at ch.qos.logback.classic.util.ContextInitializer.autoConfig(ContextInitializer.java:67)
        at ch.qos.logback.classic.spi.LogbackServiceProvider.initializeLoggerContext(LogbackServiceProvider.java:51)
        at ch.qos.logback.classic.spi.LogbackServiceProvider.initialize(LogbackServiceProvider.java:44)
        [...]
Caused by: ch.qos.logback.core.LogbackException: Unexpected filename extension of file [file:/C:/projects/]. Should be .xml
        at ch.qos.logback.classic.util.DefaultJoranConfigurator.configureByResource(DefaultJoranConfigurator.java:71)
        at ch.qos.logback.classic.util.DefaultJoranConfigurator.configure(DefaultJoranConfigurator.java:35)
        at ch.qos.logback.classic.util.ContextInitializer.invokeConfigure(ContextInitializer.java:142)
        ... 13 more