Fix empty markup handling (#536)

* not switching to Unicode-only at this moment, so make simple

Fix #408

Co-authored-by: Aleksei Stepanov <alekseis@nvidia.com>

2 files changed, 11 insertions, 1 deletions

diff --git a/urwid/tests/test_util.py b/urwid/tests/test_util.py
index eeae2f9..06de8c8 100644
--- a/urwid/tests/test_util.py
+++ b/urwid/tests/test_util.py
@@ -227,3 +227,10 @@ class PortabilityTest(unittest.TestCase):
                 f"Locale restore impossible, probably locale not supported by system (libc ignores this error).\n"
                 f"{exc}"
             )
+
+
+class TestEmptyMarkup(unittest.TestCase):
+    def test_001_empty(self):
+        text = urwid.Text('')
+        text.set_text(text.get_text())
+        self.assertEqual("", text.text)
diff --git a/urwid/util.py b/urwid/util.py
index de5bae2..9505d74 100644
--- a/urwid/util.py
+++ b/urwid/util.py
@@ -382,7 +382,10 @@ def decompose_tagmarkup(tm):
 
     tl, al = _tagmarkup_recurse(tm, None)
     # join as unicode or bytes based on type of first element
-    text = tl[0][:0].join(tl)
+    if tl:
+        text = tl[0][:0].join(tl)
+    else:
+        text = ""
 
     if al and al[-1][0] is None:
         del al[-1]