NPE logged when user tries to login without user name

[jwgmeligmeyling]

Omit these logs because they only pollute the logs

java.lang.IllegalArgumentException: null
    at com.google.common.base.Preconditions.checkArgument(Preconditions.java:76) ~[weld-se-2.1.0.Final.jar:2013-10-11 10:25]
    at nl.tudelft.ewi.devhub.server.backend.AuthenticationBackendImpl.authenticate(AuthenticationBackendImpl.java:80) ~[devhub-server.jar:na]
    at nl.tudelft.ewi.devhub.server.web.resources.RootResource.handleLogin(RootResource.java:97) ~[devhub-server.jar:na]
    at sun.reflect.GeneratedMethodAccessor456.invoke(Unknown Source) ~[na:na]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_40]
    at java.lang.reflect.Method.invoke(Method.java:497) ~[na:1.8.0_40]
    at org.jboss.resteasy.core.MethodInjectorImpl.invoke(MethodInjectorImpl.java:137) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.core.ResourceMethodInvoker.invokeOnTarget(ResourceMethodInvoker.java:296) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:250) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.core.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:237) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:356) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:179) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:220) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) [resteasy-jaxrs-3.0.10.Final.jar:na]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) [javax.servlet-api-3.1.0.jar:3.1.0]
    at org.eclipse.jetty.servlet.ServletHolder.handle(ServletHolder.java:808) [jetty-servlet-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1669) [jetty-servlet-9.2.10.v20150310.jar:9.2.10.v20150310]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:66) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterDefinition.doFilter(FilterDefinition.java:168) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:58) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterDefinition.doFilter(FilterDefinition.java:168) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:58) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterDefinition.doFilter(FilterDefinition.java:168) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:58) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterDefinition.doFilter(FilterDefinition.java:168) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:58) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterDefinition.doFilter(FilterDefinition.java:168) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:58) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterDefinition.doFilter(FilterDefinition.java:168) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:58) [guice-servlet-3.0.jar:na]
    at com.google.inject.persist.PersistFilter.doFilter(PersistFilter.java:89) [guice-persist-3.0.jar:na]
    at com.google.inject.servlet.FilterDefinition.doFilter(FilterDefinition.java:163) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.FilterChainInvocation.doFilter(FilterChainInvocation.java:58) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.ManagedFilterPipeline.dispatch(ManagedFilterPipeline.java:118) [guice-servlet-3.0.jar:na]
    at com.google.inject.servlet.GuiceFilter.doFilter(GuiceFilter.java:113) [guice-servlet-3.0.jar:na]
    at org.eclipse.jetty.servlet.ServletHandler$CachedChain.doFilter(ServletHandler.java:1652) [jetty-servlet-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.servlet.ServletHandler.doHandle(ServletHandler.java:585) [jetty-servlet-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.session.SessionHandler.doHandle(SessionHandler.java:221) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1127) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.handler.ContextHandler.doHandle(ContextHandler.java:1127) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.servlet.ServletHandler.doScope(ServletHandler.java:515) [jetty-servlet-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.session.SessionHandler.doScope(SessionHandler.java:185) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1061) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.handler.ContextHandler.doScope(ContextHandler.java:1061) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.handler.ScopedHandler.handle(ScopedHandler.java:141) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.handler.ContextHandlerCollection.handle(ContextHandlerCollection.java:215) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:97) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.Server.handle(Server.java:497) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:310) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:257) [jetty-server-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.io.AbstractConnection$2.run(AbstractConnection.java:540) [jetty-io-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:635) [jetty-util-9.2.10.v20150310.jar:9.2.10.v20150310]
    at org.eclipse.jetty.util.thread.QueuedThreadPool$3.run(QueuedThreadPool.java:555) [jetty-util-9.2.10.v20150310.jar:9.2.10.v20150310]
    at java.lang.Thread.run(Thread.java:745) [na:1.8.0_40]