FBX-60 fix ArgumentNullException when opening export window on linux (#562)

* fix ArgumentNullException on Linux when OnGUI called before export set is set

* update changelog and bump version

* reduce min coverage

Author: vkovec

.yamato/upm-ci.yml

@@ -14,7 +14,7 @@ platforms:
     image: package-ci/mac:stable
     flavor: b1.medium
 coverage:
-    minPercent: 57.6
+    minPercent: 57.5
 ---
 pack:
   name: Pack

CHANGELOG.md

@@ -1,5 +1,9 @@
 # Changes in Fbx Exporter
 
+## [4.0.0-pre.4] - 2021-01-26
+### Fixed
+- Fix ArgumentNullException on Linux when opening Export Options window.
+
 ## [4.0.0-pre.3] - 2021-01-13
 ### Changed
 - Added missing release date information to changelog.

com.unity.formats.fbx/Editor/ExportModelEditorWindow.cs

@@ -276,6 +276,18 @@ public void OnPresetSelectionChanged()
         protected bool SelectionContainsPrefabInstanceWithAddedObjects()
         {
             var exportSet = GetToExport();
+            // FBX-60 (fogbug 1307749):
+            // On Linux OnGUI() sometimes gets called a few times before
+            // the export set is set and window.show() is called.
+            // This leads to this function being called from OnGUI() with a
+            // null or empty export set, and an ArgumentNullException when
+            // creating the stack.
+            // Check that the set exists and has values before creating the stack.
+            if (exportSet == null || exportSet.Length <= 0)
+            {
+                return false;
+            }
+
             Stack<Object> stack = new Stack<Object>(exportSet);
             while (stack.Count > 0)
             {

com.unity.formats.fbx/package.json

@@ -1,7 +1,7 @@
 {
   "name": "com.unity.formats.fbx",
   "displayName": "FBX Exporter",
-  "version": "4.0.0-pre.3",
+  "version": "4.0.0-pre.4",
   "dependencies": {
     "com.unity.timeline": "1.0.0",
     "com.autodesk.fbx": "4.0.0-pre.2"