Set default location for part

- Used as "default" when creating new StockItem for that part

lib/api_form.dart

@@ -395,7 +395,7 @@ class APIFormField {
     // Render a "related field" based on the "model" type
 
     // Convert to JSON
-    Map<String, dynamic> data = item as Map<String, dynamic>;
+    var data = Map<String, dynamic>.from((item ?? {}) as Map);
 
     switch (model) {
       case "part":

lib/inventree/part.dart

@@ -139,9 +139,9 @@ class InvenTreePart extends InvenTreeModel {
       "keywords": {},
       "link": {},
 
-      // Parent category
-      "category": {
-      },
+      "category": {},
+
+      "default_location": {},
 
       "units": {},
 
@@ -242,6 +242,8 @@ class InvenTreePart extends InvenTreeModel {
     });
   }
 
+  int? get defaultLocation => jsondata["default_location"] as int?;
+
     // Get the number of stock on order for this Part
     double get onOrder => double.tryParse(jsondata["ordering"].toString()) ?? 0;
 

lib/widget/part_detail.dart

@@ -400,6 +400,12 @@ class _PartDisplayState extends RefreshableState<PartDetailWidget> {
 
     fields["part"]["hidden"] = true;
 
+    int? default_location = part.defaultLocation;
+
+    if (default_location != null) {
+      fields["location"]["value"] = default_location;
+    }
+
     InvenTreeStockItem().createForm(
         context,
         L10().stockItemCreate,