Skeleton data is optional.

spine-libgdx/src/com/esotericsoftware/spine/SkeletonBinary.java

@@ -108,15 +108,17 @@ public class SkeletonBinary {
 		DataInput input = new DataInput(file.read(512));
 		try {
 			skeletonData.hash = input.readString();
+			if (skeletonData.hash.isEmpty()) skeletonData.hash = null;
 			skeletonData.version = input.readString();
+			if (skeletonData.version.isEmpty()) skeletonData.version = null;
 			skeletonData.width = input.readFloat();
 			skeletonData.height = input.readFloat();
 
 			boolean nonessential = input.readBoolean();
 
 			if (nonessential) {
-				String imagesPath = input.readString();
-				if (imagesPath.length() > 0) skeletonData.imagesPath = imagesPath;
+				skeletonData.imagesPath = input.readString();
+				if (skeletonData.imagesPath.isEmpty()) skeletonData.imagesPath = null;
 			}
 
 			// Bones.

spine-libgdx/src/com/esotericsoftware/spine/SkeletonJson.java

@@ -95,10 +95,10 @@ public class SkeletonJson {
 		// Skeleton.
 		JsonValue skeletonMap = root.get("skeleton");
 		if (skeletonMap != null) {
-			skeletonData.hash = skeletonMap.getString("hash");
-			skeletonData.version = skeletonMap.getString("spine");
-			skeletonData.width = skeletonMap.getFloat("width");
-			skeletonData.height = skeletonMap.getFloat("height");
+			skeletonData.hash = skeletonMap.getString("hash", null);
+			skeletonData.version = skeletonMap.getString("spine", null);
+			skeletonData.width = skeletonMap.getFloat("width", 0);
+			skeletonData.height = skeletonMap.getFloat("height", 0);
 			skeletonData.imagesPath = skeletonMap.getString("images", null);
 		}