Clojurians Log v2

Beginner learning from Clojure for the Brave and True and have been stuck on the mapify function in Ch. 4. I have been able to run all the forms, including mapify in the REPL okay. When I invoke mapify in the: (first (mapify (parse (slurp filename)))) (mapify (parse (slurp filename))) I get the: java.lang.NullPointerException error on the earlier function fwpd.core/convert when I tried to trace the error. In trying to figure this out, I think I narrowed it down to being a call of the function: (defn str->int [str] (Integer. str)) Everything parses and slurps as in the book until the above mentioned call to "mapify". I have spent a great deal of time working through getting Emacs running (and configured with the multitude of out-of-date resources to some confidence I have that right, on the way, I also worked to understand Cursive in the various abandonings of Emacs, and also in using a raw lein repl. I believe it has nothing to do with the editors but with a java exception due to a lack of knowing the context of (.Integer). I had earlier gotten errors about unable to disambiguate .Integer in the context. I think this is probably a very common noob set of issues but I cannot figure it out among the many dated and slightly off topic examples in the web, slack, google groups, stack overflow, and countless blog posts. There are countless permutations on the possibilities. I need an expert's help. Expert being anyone who is ahead of me. Has anyone else run up against this and do you have any suggestions?