Thanks for noticing my issue, Hoss.
"combine" vs "merge" seem similar to me. "wrap" (if on DefaultSolrParams) or "wrapDefaults" (if not) sounds clearer to me.
I started this by putting a method in the respective class it came from, but then I noticed that SolrParams already has some handy static utility methods. Then it occurred to me that it would be convenient if the caller didn't need to know about all the classes in this package – just SolrParams with some static factory methods. It's just one class to import too. Extending this line of reasoning suggests more refactoring would be in order to create a MapSolrParams. What do you think?
RE import statements: It would be nice if there was a standard the project could agree on so we could just configure our IDEs consistently. In the mean time, I'll try to reduce import statement modifications.