Fix Document.add_path for empty groups (#170)

svgpathtools/document.py

@@ -289,7 +289,7 @@ class Document:
 
         # If given a list of strings (one or more), assume it represents
         # a sequence of nested group names
-        elif all(isinstance(elem, str) for elem in group):
+        elif len(group) > 0 and all(isinstance(elem, str) for elem in group):
             group = self.get_or_add_group(group)
 
         elif not isinstance(group, Element):

test/test_groups.py

@@ -235,4 +235,11 @@ class TestGroups(unittest.TestCase):
 
         path = parse_path(path_d)
         svg_path = doc.add_path(path, group=new_leaf)
-        self.assertEqual(path_d, svg_path.get('d'))
+        self.assertEqual(path_d, svg_path.get('d'))
+
+        # Test that paths are added to the correct group
+        new_sibling = doc.get_or_add_group(
+            ['base_group', 'new_parent', 'new_sibling'])
+        doc.add_path(path, group=new_sibling)
+        self.assertEqual(len(new_sibling), 1)
+        self.assertEqual(path_d, new_sibling[0].get('d'))