diff --git a/components/tidb_query_expr/src/impl_math.rs b/components/tidb_query_expr/src/impl_math.rs
index 4cddd5a4a37..d20a4d19f26 100644
--- a/components/tidb_query_expr/src/impl_math.rs
+++ b/components/tidb_query_expr/src/impl_math.rs
@@ -612,7 +612,7 @@ fn is_valid_base(base: IntWithSign) -> bool {
 
 fn extract_num_str(s: &str, from_base: IntWithSign) -> Option<(String, bool)> {
     let mut iter = s.chars().peekable();
-    let head = *iter.peek().unwrap();
+    let head = *iter.peek()?;
     let mut is_neg = false;
     if head == '+' || head == '-' {
         is_neg = head == '-';
@@ -1573,6 +1573,7 @@ mod tests {
             ("16九a", 10, 8, "20"),
             ("+", 10, 8, "0"),
             ("-", 10, 8, "0"),
+            ("", 2, 16, "0"),
         ];
         for (n, f, t, e) in tests {
             let n = Some(n.as_bytes().to_vec());