Debug failed loads

Signed-off-by: Jael Gu <mengjia.gu@zilliz.com>

loader.py

@@ -23,12 +23,20 @@ class TextLoader(PyOperator):
             file_path = file
         from langchain.document_loaders import UnstructuredFileLoader
         loader = UnstructuredFileLoader(file_path, mode='single', strategy='fast')
-        doc = loader.load()[0]
-        return doc.page_content
+        data = loader.load()
+        if len(data) > 0:
+            doc = data[0]
+            return doc.page_content
+        else:
+            raise RuntimeError(f'Failed to load data from {file}. Invalid output: {data}')
     
     def _from_url(self, url: str) -> str:
         from langchain.document_loaders import UnstructuredURLLoader
 
         loader = UnstructuredURLLoader(urls=[url])
-        doc = loader.load()[0]
-        return doc.page_content
+        data = loader.load()
+        if len(data) > 0:
+            doc = data[0]
+            return doc.page_content
+        else:
+            raise RuntimeError(f'Failed to load data from {url}. Invalid output: {data}')