determine the default value before apply transform

in set_data() determine the default values if necessary
before applying the transform.

Fixes #71

.gitignore

@@ -1 +1,2 @@
 node_modules
+.vscode/

src/object-mapper.js

@@ -345,12 +345,6 @@ function update_arr_ix(dest, ix, data, keys, context)
 // Set the given data into the given destination object
 function set_data(dest, key, data, context)
 {
-  // If there is a transformation function, call the function.
-  if (typeof context.transform == 'function') {
-    dest = dest || {}
-    data = context.transform(data, context.src, dest, context.srckey, context.destkey)
-  }
-
   // See if data is null and there is a default
   if (typeof context.default !== 'undefined' && (data == null || typeof data == 'undefined')) {
     // There is a default function, call the function to set the default
@@ -363,6 +357,12 @@ function set_data(dest, key, data, context)
       data = context.default
   }
 
+  // If there is a transformation function, call the function.
+  if (typeof context.transform == 'function') {
+    dest = dest || {}
+    data = context.transform(data, context.src, dest, context.srckey, context.destkey)
+  }
+
   // Set the object to the data if it is not undefined
   if (typeof data !== 'undefined' && key && key.name) {
     // Set the data if the data is not null, or if the 'allow nulls' key is set, or if there is a default (in the case of default=null, make sure to write this out)