DATACMNS-374 - Improved error handling in case of a missing repository.

In Repositories.getCrudInvoker(…) we now throw an IllegalArgumentException if we cannot find an appropriate repository for the given domain class. Previously it just blew up with a NullPointerException without a clear error message.

Original pull request: #46.

src/main/java/org/springframework/data/repository/support/Repositories.java

@@ -163,6 +163,8 @@ public class Repositories implements Iterable<Class<?>> {
 		RepositoryInformation information = getRepositoryInformationFor(domainClass);
 		Object repository = getRepositoryFor(domainClass);
 
+		Assert.notNull(repository, String.format("No repository found for domain class: %s", domainClass));
+
 		if (repository instanceof CrudRepository) {
 			return new CrudRepositoryInvoker<T>((CrudRepository<T, Serializable>) repository);
 		} else {