don't add empty text to history

src/history.rs

@@ -8,7 +8,11 @@ impl History {
     }
 
     pub fn add<S: Into<String>>(&mut self, event: S) {
-        self.events.push(event.into());
+        let text = event.into();
+        if text.is_empty() {
+            return;
+        }
+        self.events.push(text);
     }
 
     pub fn look_back(&self, idx: usize) -> Option<&str> {