fix: Change the replacement symbol for masked entity (#188)

* fix: Change the replacement symbol for masked entity

* Apply suggestion from @gemini-code-assist[bot]

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

---------

Co-authored-by: beanbun <yuanzhonghang@pjlab.org.cn>
Co-authored-by: chenzihong <58508660+ChenZiHong-Gavin@users.noreply.github.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: 4 people

graphgen/models/generator/masked_fill_in_blank_generator.py

@@ -115,7 +115,7 @@ async def generate(
         match = re.search(mask_pattern, context)
         if match:
             gth = match.group(0)
-            masked_context = mask_pattern.sub("___", context)
+            masked_context = mask_pattern.sub("{ }", context)
         else:
             logger.debug(
                 "Regex Match Failed!\n"