Return empty iterator for empty string

instant-segment/src/lib.rs

@@ -62,7 +62,11 @@ impl Segmenter {
         input: &str,
         search: &'a mut Search,
     ) -> Result<impl Iterator<Item = &'a str> + ExactSizeIterator, InvalidCharacter> {
-        SegmentState::new(Ascii::new(input)?, self, search).run();
+        let state = SegmentState::new(Ascii::new(input)?, self, search);
+        if !input.is_empty() {
+            state.run();
+        }
+
         Ok(search.result.iter().map(|v| v.as_str()))
     }
 

instant-segment/src/test_cases.rs

@@ -3,6 +3,8 @@ use crate::{Search, Segmenter};
 /// Run a segmenter against the built-in test cases
 pub fn run(segmenter: &Segmenter) {
     let mut search = Search::default();
+    assert_eq!(segmenter.segment("", &mut search).unwrap().len(), 0);
+
     let mut success = true;
     for test in TEST_CASES.iter().copied() {
         success &= assert_segments(test, &mut search, segmenter);