Add is_empty method to Roles

src/pcd.rs

@@ -482,6 +482,10 @@ impl Roles {
         Roles(roles)
     }
 
+    pub fn is_empty(&self) -> bool {
+        self.0.is_empty()
+    }
+
     pub fn to_bytes(&self) -> Result<Vec<u8>> {
         serde_json::to_vec(&self.0).map_err(|e| Error::msg(e.to_string()))
     }