descriptor: don't accept strings of the form tr(<key>,)

src/descriptor/tr.rs

@@ -587,9 +587,6 @@ fn parse_tr_tree(s: &str) -> Result<expression::Tree, Error> {
             return Err(Error::Unexpected("invalid taproot internal key".to_string()));
         }
         let internal_key = expression::Tree { name: key.name, args: vec![] };
-        if script.is_empty() {
-            return Ok(expression::Tree { name: "tr", args: vec![internal_key] });
-        }
         let (tree, rest) = expression::Tree::from_slice_delim(script, 1, '{')?;
         if rest.is_empty() {
             Ok(expression::Tree { name: "tr", args: vec![internal_key, tree] })
@@ -770,6 +767,14 @@ mod tests {
         desc.replace(&[' ', '\n'][..], "")
     }
 
+    #[test]
+    fn regression_736() {
+        crate::Descriptor::<crate::DescriptorPublicKey>::from_str(
+            "tr(0000000000000000000000000000000000000000000000000000000000000002,)",
+        )
+        .unwrap_err();
+    }
+
     #[test]
     fn for_each() {
         let desc = descriptor();