Extend content exceptions in group encoding

xmlschema/validators/groups.py

@@ -1142,7 +1142,7 @@ def iter_encode(self, obj: ElementData, validation: str = 'lax', **kwargs: Any)
         over_max_depth = 'max_depth' in kwargs and kwargs['max_depth'] <= level
 
         content: Iterable[Any]
-        if obj.content is None:
+        if not obj.content:
             content = []
         elif isinstance(obj.content, MutableMapping) or kwargs.get('unordered'):
             content = ModelVisitor(self).iter_unordered_content(
@@ -1151,6 +1151,12 @@ def iter_encode(self, obj: ElementData, validation: str = 'lax', **kwargs: Any)
         elif not isinstance(obj.content, MutableSequence):
             wrong_content_type = True
             content = []
+        elif not isinstance(obj.content[0], tuple):
+            if len(obj.content) > 1 or text is not None:
+                wrong_content_type = True
+            else:
+                text = raw_xml_encode(obj.content[0])
+            content = []
         elif converter.losslessly:
             content = obj.content
         else: