fix teacher properties

Author: SKairinos

codeforlife/user/models/teacher.py

@@ -175,9 +175,6 @@ def teacher_as_type(
     Returns:
         An instance of the typed teacher.
     """
-    # TODO: remove in new schema
-    if teacher is None:
-        return None
 
     return typed_teacher_class(
         pk=teacher.pk,

codeforlife/user/models/user.py

@@ -313,7 +313,9 @@ def teacher(self):
         # pylint: disable-next=import-outside-toplevel
         from .teacher import SchoolTeacher, teacher_as_type
 
-        return teacher_as_type(super().teacher, SchoolTeacher)
+        teacher = super().teacher
+
+        return teacher_as_type(teacher, SchoolTeacher) if teacher else None
 
 
 # pylint: disable-next=missing-class-docstring,too-few-public-methods
@@ -341,7 +343,9 @@ def teacher(self):
         # pylint: disable-next=import-outside-toplevel
         from .teacher import AdminSchoolTeacher, teacher_as_type
 
-        return teacher_as_type(super().teacher, AdminSchoolTeacher)
+        teacher = super().teacher
+
+        return teacher_as_type(teacher, AdminSchoolTeacher) if teacher else None
 
 
 # pylint: disable-next=missing-class-docstring,too-few-public-methods
@@ -369,7 +373,11 @@ def teacher(self):
         # pylint: disable-next=import-outside-toplevel
         from .teacher import NonAdminSchoolTeacher, teacher_as_type
 
-        return teacher_as_type(super().teacher, NonAdminSchoolTeacher)
+        teacher = super().teacher
+
+        return (
+            teacher_as_type(teacher, NonAdminSchoolTeacher) if teacher else None
+        )
 
 
 # pylint: disable-next=missing-class-docstring,too-few-public-methods
@@ -395,7 +403,9 @@ def teacher(self):
         # pylint: disable-next=import-outside-toplevel
         from .teacher import NonSchoolTeacher, teacher_as_type
 
-        return teacher_as_type(super().teacher, NonSchoolTeacher)
+        teacher = super().teacher
+
+        return teacher_as_type(teacher, NonSchoolTeacher) if teacher else None
 
 
 # pylint: disable-next=missing-class-docstring,too-few-public-methods