Throw a SolrRuntimeException when a SolrServerException happens, rather than returning null (which results in a NullPointerException later on in some cases, such as the bug encountered here)
Check whether the result is null in downloadImages controller and throw appropriate error if it is.
Removed unused method in SolrSearchService, and some cleanup
https://unclibrary.atlassian.net/browse/BXC-4664