FIX: Merge-JsonSimpleMap

- First time hash is undefined, copying it is not a good
    approach - instead, create a new empty hash and
    copy values in

core/JsonHelpers.ps1

@@ -120,22 +120,21 @@ function Merge-JsonSimpleMap
   if (!$Destination.$Name)
   {
     $Destination |
-      Add-Member -Name $Name -Value $SimpleMap -MemberType NoteProperty
+      Add-Member -Name $Name -Value ([PSCustomObject]@{}) -MemberType NoteProperty
   }
-  else
-  {
+
   $currentHash = $Destination.$Name
   $SimpleMap.PSObject.Properties |
     % {
-        if (!$currentHash.($_.Name))
+      $key = $_.Name
+      if (!$currentHash.$key)
       {
         $currentHash |
-            Add-Member -Name ($_.Name) -Value $_.Value -MemberType NoteProperty
+          Add-Member -Name $key -Value $_.Value -MemberType NoteProperty
       }
       else
       {
-          $currentHash.($_.Name) = $_.Value
-        }
+        $currentHash.$key = $_.Value
       }
     }
 }