Update src/DAG2ppt.py

src/DAG2ppt.py

@@ -712,7 +712,14 @@ def generate_ppt(
             continue
 
         norm_node = _normalize_node(node)
-        template_file = norm_node.get("template", "").strip()
+
+        raw_template = norm_node.get("template")
+        # Check if raw_template exists and is not empty after stripping whitespace
+        if raw_template and raw_template.strip():
+            template_file = raw_template.strip()
+        else:
+            # Assign default value when template is None, empty string "", or only whitespace
+            template_file = "T1_TextOnly.html"
         
         # Skip if no template or explicitly null/empty
         if not template_file or template_file.lower() == "null":