PICARD-2958: Handle gettext being called with empty string

Calling gettext("") by default returns the header of the PO file for the
current locale. This is unexpected. Return an empty string instead.

picard/i18n.py

@@ -196,6 +196,10 @@ def setup_gettext(localedir, ui_language=None, logger=None):
 
 def gettext(message: str) -> str:
     """Translate the messsage using the current translator."""
+    # Calling gettext("") by default returns the header of the PO file for the
+    # current locale. This is unexpected. Return an empty string instead.
+    if message == "":
+        return message
     return _translation['main'].gettext(message)
 
 

test/test_i18n.py

@@ -85,6 +85,10 @@ def test_existing_locales(self):
         # self.assertEqual('Französisch', gettext_constants('French'))
         self.assertEqual('Frankreich', gettext_countries('France'))
 
+    def test_gettext_handles_empty_string(self):
+        setup_gettext(localedir, 'fr')
+        self.assertEqual('', _(''))
+
     def test_sort_key(self):
         setup_gettext(localedir, 'de')
         self.assertTrue(sort_key('äb') < sort_key('ac'))