From d2a7c86dc33d6def6dba44f6ed2b71e8a1644130 Mon Sep 17 00:00:00 2001
From: Malte <ms@mieo.de>
Date: Mon, 22 Jun 2020 17:09:05 +0200
Subject: [PATCH] Check if `text` is set to avoid IndexError (#4209)

Fix for https://github.com/huggingface/transformers/issues/3809
---
 src/transformers/tokenization_roberta.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/transformers/tokenization_roberta.py b/src/transformers/tokenization_roberta.py
index 837639eac4..381ab2b5a6 100644
--- a/src/transformers/tokenization_roberta.py
+++ b/src/transformers/tokenization_roberta.py
@@ -236,7 +236,7 @@ class RobertaTokenizer(GPT2Tokenizer):
             add_prefix_space = kwargs["add_prefix_space"]
         else:
             add_prefix_space = add_special_tokens
-        if add_prefix_space and not text[0].isspace():
+        if add_prefix_space and len(text) > 0 and not text[0].isspace():
             text = " " + text
         return text