Merge branch '4.1' into 4.2-beta

spine-unity/Assets/Spine/Runtime/spine-unity/Mesh Generation/MeshGenerator.cs

@@ -491,6 +491,8 @@ namespace Spine.Unity {
 			SubmeshInstruction[] wsii = workingSubmeshInstructions.Items;
 			for (int i = 0; i < workingSubmeshInstructions.Count; i++) {
 				Material material = wsii[i].material;
+				if (material == null) continue;
+
 				Material overrideMaterial;
 				if (customMaterialOverride.TryGetValue(material, out overrideMaterial))
 					wsii[i].material = overrideMaterial;

spine-unity/Assets/Spine/package.json

@@ -2,7 +2,7 @@
 	"name": "com.esotericsoftware.spine.spine-unity",
 	"displayName": "spine-unity Runtime",
 	"description": "This plugin provides the spine-unity runtime core.",
-	"version": "4.2.39",
+	"version": "4.2.40",
 	"unity": "2018.3",
 	"author": {
 		"name": "Esoteric Software",