sort: handle empty merge inputs

src/uu/sort/src/merge.rs

@@ -194,13 +194,15 @@ fn merge_without_limit<M: MergeInput + 'static, F: Iterator<Item = M>>(
     let mut mergeable_files = vec![];
 
     for (file_number, receiver) in loaded_receivers.into_iter().enumerate() {
+        if let Ok(chunk) = receiver.recv() {
             mergeable_files.push(MergeableFile {
-            current_chunk: Rc::new(receiver.recv().unwrap()),
+                current_chunk: Rc::new(chunk),
                 file_number,
                 line_idx: 0,
                 receiver,
             })
         }
+    }
 
     FileMerger {
         heap: binary_heap_plus::BinaryHeap::from_vec_cmp(

tests/by-util/test_sort.rs

@@ -1039,3 +1039,12 @@ fn test_output_device() {
         .pipe_in("input")
         .succeeds();
 }
+
+#[test]
+fn test_merge_empty_input() {
+    new_ucmd!()
+        .args(&["-m", "empty.txt"])
+        .succeeds()
+        .no_stderr()
+        .no_stdout();
+}