Fix checking for file existence only when the options are set.

src/cipher_analytical_machine/cli.clj

@@ -69,10 +69,12 @@
       (map-has-keys? options [:message, :message-file])
       {:exit-message (error-msg ["You can't use message and message-file options at the same time!!!"])}
 
-      (file/is-file-not-exists? (:message-file options))
+      (and (contains? options :message-file)
+           (file/is-file-not-exists? (:message-file options)))
       {:exit-message (error-msg ["Please, check the path to the message file!!!"])}
 
-      (file/is-file-exists? (:output-file options))
+      (and (contains? options :output-file)
+           (file/is-file-exists? (:output-file options)))
       {:exit-message (error-msg ["Please, choose another file!!! Overwriting was prevented!!!"])}
 
       (and (map-has-keys? options [:cipher, :key])