patch 8.0.0351: no test for concatenating an empty string
Problem: No test for concatenating an empty string that results from out of
bounds indexing.
Solution: Add a simple test.
diff --git a/src/testdir/test_expr.vim b/src/testdir/test_expr.vim
index e5c918c..80cdc1b 100644
--- a/src/testdir/test_expr.vim
+++ b/src/testdir/test_expr.vim
@@ -473,3 +473,8 @@
call setmatches(set)
call assert_equal(exp, getmatches())
endfunc
+
+func Test_empty_concatenate()
+ call assert_equal('b', 'a'[4:0] . 'b')
+ call assert_equal('b', 'b' . 'a'[4:0])
+endfunc