🐛 fix amount display (#246)

Author: sebastianMindee

mindee/parsing/standard/amount.py

@@ -39,4 +39,4 @@ def __init__(
         self._set_position(raw_prediction)
 
     def __str__(self) -> str:
-        return float_to_string(self.value)
+        return float_to_string(self.value) if self.value is not None else ""