better assert message

src/boxerror.js

@@ -10,7 +10,7 @@ exports = module.exports = BoxError;
 
 function BoxError(reason, errorOrMessage, extra = {}) {
     assert.strictEqual(typeof reason, 'string');
-    assert(errorOrMessage instanceof Error || typeof errorOrMessage === 'string');
+    assert(errorOrMessage instanceof Error || typeof errorOrMessage === 'string', `string: ${errorOrMessage} type: ${typeof errorOrMessage} json: ${JSON.stringify(errorOrMessage)}`);
     assert(typeof extra === 'object');
 
     Error.call(this);