tweak to custom data function check.

Author: ctalkington

lib/core.js

@@ -397,10 +397,12 @@ Archiver.prototype.bulk = function(mappings) {
       }
 
       try {
-        entryData = dataFunction ? dataFunction(entryData) : entryData;
+        if (dataFunction) {
+          entryData = dataFunction(entryData);
 
-        if (dataFunction && typeof entryData !== 'object') {
-          throw new Error('bulk: invalid data returned from custom function');
+          if (typeof entryData !== 'object') {
+            throw new Error('bulk: invalid data returned from custom function');
+          }
         }
       } catch(e) {
         self.emit('error', e);
@@ -453,10 +455,12 @@ Archiver.prototype.directory = function(dirpath, destpath, data) {
         entryData.stats = file.stats;
 
         try {
-          entryData = dataFunction ? dataFunction(entryData) : entryData;
+          if (dataFunction) {
+            entryData = dataFunction(entryData);
 
-          if (dataFunction && typeof entryData !== 'object') {
-            throw new Error('directory: invalid data returned from custom function');
+            if (typeof entryData !== 'object') {
+              throw new Error('directory: invalid data returned from custom function');
+            }
           }
         } catch(e) {
           self.emit('error', e);