From 7e5bb2ef4a231517ffeca288b247cab3161f77d3 Mon Sep 17 00:00:00 2001
From: Jeroen Van Goey <j.vangoey@instadeep.com>
Date: Fri, 19 Jun 2026 21:58:54 +0200
Subject: [PATCH] Handle empty ProForma formulas

---
 mzcore/src/chemistry/formula/formula.rs   | 5 +++++
 mzcore/src/chemistry/formula/pro_forma.rs | 2 +-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/mzcore/src/chemistry/formula/formula.rs b/mzcore/src/chemistry/formula/formula.rs
index c6a039e6..c2b19e1f 100644
--- a/mzcore/src/chemistry/formula/formula.rs
+++ b/mzcore/src/chemistry/formula/formula.rs
@@ -352,5 +352,10 @@ mod tests {
             MolecularFormula::pro_forma::<false, true>("(empty)"),
             MolecularFormula::pro_forma::<false, true>("H0")
         );
+        assert_eq!(
+            MolecularFormula::pro_forma::<false, true>(""),
+            MolecularFormula::pro_forma::<false, true>("H0")
+        );
+        assert!(MolecularFormula::pro_forma::<false, false>("").is_err());
     }
 }
diff --git a/mzcore/src/chemistry/formula/pro_forma.rs b/mzcore/src/chemistry/formula/pro_forma.rs
index 6b92d8a0..f5d66788 100644
--- a/mzcore/src/chemistry/formula/pro_forma.rs
+++ b/mzcore/src/chemistry/formula/pro_forma.rs
@@ -75,7 +75,7 @@ impl MolecularFormula {
         range: impl RangeBounds<usize>,
     ) -> Result<Self, BoxedError<'a, BasicKind>> {
         let (mut index, end) = range.bounds(value.len().saturating_sub(1));
-        if index > end || &value[index..=end] == "(empty)" {
+        if value.is_empty() || index > end || value.get(index..=end) == Some("(empty)") {
             return if ALLOW_EMPTY {
                 Ok(Self::default())
             } else {