Fixed #20618 -- Fixed regression in `BoundField.label_tag`.

django/forms/forms.py

@@ -518,8 +518,7 @@ class BoundField(object):
         """
         contents = contents or self.label
         # Only add the suffix if the label does not end in punctuation.
-        if self.form.label_suffix:
-            if contents[-1] not in ':?.!':
+        if self.form.label_suffix and contents and contents[-1] not in ':?.!':
             contents = format_html('{0}{1}', contents, self.form.label_suffix)
         widget = self.field.widget
         id_ = widget.attrs.get('id') or self.auto_id

tests/forms_tests/tests/test_forms.py

@@ -1863,3 +1863,10 @@ class FormsTestCase(TestCase):
         form = SomeForm()
         self.assertHTMLEqual(form['custom'].label_tag(), '<label for="custom_id_custom">Custom:</label>')
         self.assertHTMLEqual(form['empty'].label_tag(), '<label>Empty:</label>')
+
+    def test_boundfield_empty_label(self):
+        class SomeForm(Form):
+            field = CharField(label='')
+        boundfield = SomeForm()['field']
+
+        self.assertHTMLEqual(boundfield.label_tag(), '<label for="id_field"></label>')