diff --git a/pymatgen/io/validation/validation.py b/pymatgen/io/validation/validation.py
index 9d7d812..51e5815 100644
--- a/pymatgen/io/validation/validation.py
+++ b/pymatgen/io/validation/validation.py
@@ -53,7 +53,7 @@ class ValidationDoc(EmmetBaseModel):
     Validation document for a VASP calculation
     """
 
-    task_id: MPID | None = Field(None, description="The task_id for this validation document")
+    task_id: MPID = Field(None, description="The task_id for this validation document")
 
     valid: bool = Field(False, description="Whether this task is valid or not")