SEC-1922: Improve error-message when user property file has wrong format

David J. M. Karlsen (Migrated from SEC-1922) said:

If the user details file has the wrong format (I had a configline which was "OK" but forgot to chuck in the '"' character) you will get this stacktrace:

Caused by: java.lang.NullPointerException: null
        at org.springframework.security.provisioning.InMemoryUserDetailsManager.<init>(InMemoryUserDetailsManager.java:52) ~[spring-security-core-3.1.0.RELEASE.jar:3.1.0.RELEASE]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.6.0]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:56) ~[na:1.6.0]
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:39) ~[na:1.6.0]
        at java.lang.reflect.Constructor.newInstance(Constructor.java:527) ~[na:1.6.0]
        at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:126) ~[spring-beans-3.0.7.RELEASE.jar:3.0.7.RELEASE]
        ... 101 common frames omitted

it would be nicer to say that the file has an unexpected format.

Start in org.springframework.security.provisioning.InMemoryUserDetailsManager at the constructor line shown in the stack trace, and inspect how malformed user-detail configuration is handled. Reproduce the wrong-format input described in the issue; done means it reports an unexpected file format instead of a NullPointerException.