SDP throws NPE if the index includes no commits, but snapshot() is called. This is an extreme case, but can happen if one takes snapshots (for backup purposes for example) in a separate code segment than indexing, and does not know if commit was called or not.
I think we should throw an IllegalStateException instead of falling on NPE, w/ a descriptive message. Alternatively, we can just return null and document it ... But I prefer the ISE instead. What do you think? Shai
