Update utils/enrollment.py

Use grade: str = Field(default=Grade.A_PLUS)

utils/enrollment.py

@@ -1,4 +1,4 @@
-from typing import Optional, Union
+from typing import Optional
 from utils.enums.grade import Grade
 
 from .student import Student
@@ -14,13 +14,13 @@ class Enrollment(SQLModel, table=True):
         id: (int): The enrollment ID
         student_id (str): The ID of the student who is enrolled in the course.
         course_id (str): The ID of the course in which the student is enrolled.
-        grade (Union[str, Grade]): The grade assigned to the student for the course. Default if NO_GRADE with enum value of None if no grade has been assigned yet.
+        grade (str): The grade assigned to the student for the course. Default if NO_GRADE with enum value of None if no grade has been assigned yet.
     """
 
     id: int = Field(primary_key=True)
     student_id: str = Field(foreign_key="student.id")
     course_id: str = Field(foreign_key="course.id")
-    grade: Union[str, Grade] = Field(default=Grade.A_PLUS)
+    grade: str = Field(default=Grade.A_PLUS)
 
     course: "Course" = Relationship(
         back_populates="enrollments")