Exception when nil stdout is print

[arichiardi]

Hello @flyboarder!

While working on the less compiler, I have noticed that when I use :show true sometimes I get:

Executing Process: /home/arichiardi/git/ar-website/node_modules/less/bin/lessc
                                java.lang.Thread.run              Thread.java:  748
  java.util.concurrent.ThreadPoolExecutor$Worker.run  ThreadPoolExecutor.java:  624
   java.util.concurrent.ThreadPoolExecutor.runWorker  ThreadPoolExecutor.java: 1149
                 java.util.concurrent.FutureTask.run          FutureTask.java:  266
                                                 ...                               
                 clojure.core/binding-conveyor-fn/fn                 core.clj: 1938
                                   boot.core/boot/fn                 core.clj: 1031
                                 boot.core/run-tasks                 core.clj: 1021
                      boot.task.built-in/fn/fn/fn/fn             built_in.clj:  632
                 degree9.boot-exec/eval3376/fn/fn/fn            boot_exec.clj:   30
                 degree9.boot-exec/eval3419/fn/fn/fn            boot_exec.clj:   78
                      boot.task.built-in/fn/fn/fn/fn             built_in.clj:  632 (repeats 2 times)
boot.user$eval5027$fn__5028$fn__5033$fn__5034.invoke                         :  110
                 degree9.boot-exec/eval3419/fn/fn/fn            boot_exec.clj:   79
                         degree9.boot-exec/exec-impl            boot_exec.clj:   63
                                                 ...                               
                                      boot.util/info                 util.clj:  142
                                    boot.util/print*                 util.clj:   75
                                  clojure.core/apply                 core.clj:  646
                                                 ...                               
                                 clojure.core/format                 core.clj: 5527
                                 clojure.core/format                 core.clj: 5533
                             java.lang.String.format              String.java: 2940
                          java.util.Formatter.format           Formatter.java: 2455
                          java.util.Formatter.format           Formatter.java: 2501
                           java.util.Formatter.parse           Formatter.java: 2547
                     java.util.regex.Pattern.matcher             Pattern.java: 1093
                      java.util.regex.Matcher.<init>             Matcher.java:  229
                       java.util.regex.Matcher.reset             Matcher.java:  309
               java.util.regex.Matcher.getTextLength             Matcher.java: 1283

The files gets generated but it seems that this line needs to be skipped if stdout is nil.

Leaving this open for now, I might have time later for a simple fix.