diff --git a/shared/comm-lib/src/tools.rs b/shared/comm-lib/src/tools.rs
--- a/shared/comm-lib/src/tools.rs
+++ b/shared/comm-lib/src/tools.rs
@@ -46,13 +46,17 @@
 ///     }
 /// }
 /// ```
-pub struct Defer<'s>(Option<Box<dyn FnOnce() + 's>>);
+pub struct Defer<'s>(Option<Box<dyn FnOnce() + 's + Send>>);
 
 impl<'s> Defer<'s> {
-  pub fn new(f: impl FnOnce() + 's) -> Self {
+  pub fn new(f: impl FnOnce() + 's + Send) -> Self {
     Self(Some(Box::new(f)))
   }
 
+  pub fn empty() -> Self {
+    Self(None)
+  }
+
   /// Consumes the value, without calling the provided function
   ///
   /// # Example