Where is my Null Pointer Exception - Clojure edition

Question

I am getting the following stacktrace when running the command: lein run "this is the other different thing" "this,different,other"

Stacktrace

Exception in thread "main" java.lang.NullPointerException, compiling:(/private/var/folders/y8/6lt_81xn47d4n2k641z52rg00000gn/T/form-init8328218573408236617.clj:1:125)
    at clojure.lang.Compiler.load(Compiler.java:7391)
    at clojure.lang.Compiler.loadFile(Compiler.java:7317)
    at clojure.main$load_script.invokeStatic(main.clj:275)
    at clojure.main$init_opt.invokeStatic(main.clj:277)
    at clojure.main$init_opt.invoke(main.clj:277)
    at clojure.main$initialize.invokeStatic(main.clj:308)
    at clojure.main$null_opt.invokeStatic(main.clj:342)
    at clojure.main$null_opt.invoke(main.clj:339)
    at clojure.main$main.invokeStatic(main.clj:421)
    at clojure.main$main.doInvoke(main.clj:384)
    at clojure.lang.RestFn.invoke(RestFn.java:421)
    at clojure.lang.Var.invoke(Var.java:383)
    at clojure.lang.AFn.applyToHelper(AFn.java:156)
    at clojure.lang.Var.applyTo(Var.java:700)
    at clojure.main.main(main.java:37)
Caused by: java.lang.NullPointerException
    at clojure.string$replace.invokeStatic(string.clj:101)
    at clojure.string$replace.invoke(string.clj:75)
    at redact.core$redact_doc.invokeStatic(core.clj:12)
    at redact.core$redact_doc.invoke(core.clj:7)
    at redact.core$_main.invokeStatic(core.clj:54)
    at redact.core$_main.doInvoke(core.clj:50)
    at clojure.lang.RestFn.invoke(RestFn.java:421)
    at clojure.lang.Var.invoke(Var.java:383)
    at user$eval5.invokeStatic(form-init8328218573408236617.clj:1)
    at user$eval5.invoke(form-init8328218573408236617.clj:1)
    at clojure.lang.Compiler.eval(Compiler.java:6927)
    at clojure.lang.Compiler.eval(Compiler.java:6917)
    at clojure.lang.Compiler.load(Compiler.java:7379)
    ... 14 more

And here is my code:

(ns redact.core
  (:gen-class)
  (:require [clojure.java.io :as io]
            [clojure.string :as str]
))

(defn redact-doc
  ;; Reads the file line by line and redacts all the matched words
  ([target stoplist]
   (if (empty? stoplist)
     (str/trim target)
     (redact-doc (str/replace target (re-pattern (str "\\s(" (first stoplist) ")(\\s|$)")) " REDACTED ") (rest stoplist))))
  )

(defn get-target-text
  ;; Takes a vector of args and returns a String of a text file or and sentances
  ([args] (get-target-text args ""))
  ([args result]
   (if (empty? args)
     result
     (get-target-text (rest args) (if (boolean (re-find #"(.+\.[^csv\s])" (first args)))
                                    (str result (slurp (first args)))
                                    (if (not (boolean (re-find #"(.+\.csv|.+,.+)" (first args))))
                                      (if (boolean (re-find #"\s" (str/trim (first args))))
                                        (str result (first args) " ")))))))
 )

(defn read-csv
  ;; Takes in a filename and returns a vector of the csv values
  [file-name]
  (str/split (with-open [rdr (io/reader file-name)]
     (doall (reduce str (line-seq rdr)))) #","))

(defn gen-stoplist
  ;; Generates the stoplist for words to be redacted
  ([args] (gen-stoplist args []))
  ([args stoplist]
   (if (empty? args)
     stoplist
     (gen-stoplist (rest args) (if (boolean (re-find #"(.+\.csv)" (first args)))
                                 (into [] (concat stoplist (read-csv (first args))))
                                 (if (boolean (re-find #"(.+\..[^csv\s])" (first args)))
                                   stoplist
                                   (if (boolean (re-find #"(.*,.*)" (first args))) 
                                     (into [] (concat stoplist (str/split (first args) #",")))
                                     (if (boolean (re-find #"(\s)" (str/trim (first args))))
                                       stoplist
                                       (into [] (concat stoplist [(first args)] ))))))))))

(defn -main
  ([& args]
   (def stoplist (gen-stoplist args))
   (def target-text (get-target-text args))
   (println (redact-doc target-text stoplist)))
)

I have been staring at this trying to figure out what is causing the issue. I have tested all of the methods independently on the REPL and they all seem to work but the (-main) method is throwing a null pointer exception on the str/replace call....just not sure why. Any help you can give is much appreciated. Thanks!

target-text in your main method is nil. (get-target-text ["this is the other different thing" "this,different,other"]) returns nil. — Viktor K.
– Viktor K., Commented Jul 30, 2016 at 6:05

Tim X · Accepted Answer · 2016-07-30 07:22:24Z

There is a fair bit about your code which is not really correct. My guess is that our getting that call because your calling a function which is expecting a value and is getting a nil passed in - my guess would be one of the string functions.

your function definitions are not quite right. If your function only has a single 'signature' then you don't need the additional brackets. You should also use let bindings inside rather than def. e.g.

(defn -main
    [& args]
    (let [stoplist (gen-stoplist args)
          target-text (get-target-text args))]
      (println (redact-doc target-text stoplist)))

Your code is not passing what you think to gen-stoplist or get-target-text. I suspect the null pointer is because of the call to str/trim being passed a nil rather than a string.

My suggestion would be to open a repl and interact with it using some println in your functions to look at what is getting parsed in.

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