Don't set origin at all if it doesn't exist.

lib/sb3.js

@@ -126,9 +126,11 @@ const extensions = function (list) {
 };
 
 const metadata = function (meta) {
-    return {
-        origin: meta.origin ? meta.origin : ''
-    };
+    let obj = {};
+    if (meta.origin) {
+        obj.origin = meta.origin;
+    }
+    return obj;
 };
 
 module.exports = function (project, callback) {

test/unit/sb3.js

@@ -140,7 +140,7 @@ test('defalt (binary)', t => {
         t.deepEqual(result.extensions.id, []);
 
         t.type(result.meta, 'object');
-        t.equal(result.meta.origin, '');
+        t.deepEqual({}, result.meta);
 
         t.end();
     });