Fix for #52 NPE on submitting empty login form

Changes to be committed:
	modified:   src/main/java/nl/tudelft/ewi/devhub/server/backend/AuthenticationBackendImpl.java
	modified:   src/main/java/nl/tudelft/ewi/devhub/server/web/resources/RootResource.java
Merge pull request #54 from JWGmeligMeyling/nle-login

Fix for #52 NPE on submitting empty login form