change data type in models

models.py

@@ -1,17 +1,18 @@
 from pydantic import BaseModel, Field
 from datetime import date
-from typing import List, Optional, Any
+from typing import List, Union, Any
+
 
 class Experience(BaseModel):
-    start: Optional[date] = Field(None)
-    end: Optional[date] = Field(None)
+    start: Union[date, None] = Field(default=None)
+    end: Union[date, None] = Field(default=None)
     designation: str = Field(...)
     company: str = Field(...)
     experience_description: str = Field(...)
 
 class Education(BaseModel):
-    start: Optional[date] = Field(None)
-    end: Optional[date] = Field(None)
+    start: Union[date, None] = Field(default=None)
+    end: Union[date, None] = Field(default=None)
     major: str = Field(...)
     campus: str = Field(...)
     GPA: float = Field(...)