Index: ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/Activity.vb
===================================================================
diff -u -r1733 -r1737
--- ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/Activity.vb	(.../Activity.vb)	(revision 1733)
+++ ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/Activity.vb	(.../Activity.vb)	(revision 1737)
@@ -32,12 +32,12 @@
     End Sub
 
     ''' <inheritdoc/>
-    Public Sub StopActivity(employee As IEmployee) Implements IActivityActions.StopActivity
-        State.StopActivity(employee)
+    Public Sub StopActivity() Implements IActivityActions.StopActivity
+        State.StopActivity()
     End Sub
 
     ''' <inheritdoc/>
-    Public Sub FinishActivity(employee As IEmployee) Implements IActivityActions.FinishActivity
-        State.FinishActivity(employee)
+    Public Sub FinishActivity() Implements IActivityActions.FinishActivity
+        State.FinishActivity()
     End Sub
 End Class
Index: ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityDefaultedState.vb
===================================================================
diff -u -r1734 -r1737
--- ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityDefaultedState.vb	(.../ActivityDefaultedState.vb)	(revision 1734)
+++ ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityDefaultedState.vb	(.../ActivityDefaultedState.vb)	(revision 1737)
@@ -13,6 +13,10 @@
 
     ''' <inheritdoc/>
     Public Overrides Sub StartActivity(employee As IEmployee)
+        If IsNothing(employee) Then
+            'Nothing employee.
+            Throw New Exception($"The employee can't be nothing when starting an activity from defaulted state.")
+        End If
         'Update employee.
         employee.CurrentActivity = me.Activity
         'Change state.
Index: ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityStartedState.vb
===================================================================
diff -u -r1735 -r1737
--- ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityStartedState.vb	(.../ActivityStartedState.vb)	(revision 1735)
+++ ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityStartedState.vb	(.../ActivityStartedState.vb)	(revision 1737)
@@ -24,22 +24,12 @@
     End Function
 
     ''' <inheritdoc/>
-    Public Overrides Sub StopActivity(employee As IEmployee)
-        If Not CurrentEmployee.Equals(employee) Then
-            'Different employee.
-            Throw New Exception($"A different employee can't stop a started activity. Current activity belongs to {employee.ToString()}")
-        End If
+    Public Overrides Sub StopActivity()
         Activity.State = New ActivityStoppedState(Me)
     End Sub
 
     ''' <inheritdoc/>
-    Public Overrides Sub FinishActivity(employee As IEmployee)
-        If Not CurrentEmployee.Equals(employee) Then
-            'Different employee.
-            Throw New Exception($"A different employee can't finish a started activity. Current activity belongs to {employee.ToString()}")
-        End If
-        'Update employee.
-        employee.CurrentActivity = Me.Activity
+    Public Overrides Sub FinishActivity()
         'Update state.
         Activity.State = New ActivityFinishedState(Me)
     End Sub
Index: ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/IActivityActions.vb
===================================================================
diff -u -r1729 -r1737
--- ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/IActivityActions.vb	(.../IActivityActions.vb)	(revision 1729)
+++ ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/IActivityActions.vb	(.../IActivityActions.vb)	(revision 1737)
@@ -8,12 +8,10 @@
     ''' <summary>
     ''' The employee stops the activity.
     ''' </summary>
-    ''' <param name="employee"></param>
-    Sub StopActivity(employee As IEmployee)
+    Sub StopActivity()
 
     ''' <summary>
     ''' The employee finishes the activity.
     ''' </summary>
-    ''' <param name="employee"></param>
-    Sub FinishActivity(employee As IEmployee)
+    Sub FinishActivity()
 End Interface
Index: ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityState.vb
===================================================================
diff -u -r1735 -r1737
--- ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityState.vb	(.../ActivityState.vb)	(revision 1735)
+++ ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityState.vb	(.../ActivityState.vb)	(revision 1737)
@@ -30,12 +30,12 @@
     End Sub
 
     ''' <inheritdoc/>
-    Public Overridable Sub StopActivity(employee As IEmployee) Implements IActivityActions.StopActivity
+    Public Overridable Sub StopActivity() Implements IActivityActions.StopActivity
         Throw New Exception("Can't stop the activity in this state.")
     End Sub
 
     ''' <inheritdoc/>
-    Public Overridable Sub FinishActivity(employee As IEmployee) Implements IActivityActions.FinishActivity
+    Public Overridable Sub FinishActivity() Implements IActivityActions.FinishActivity
         Throw New Exception("Can't finish the activity in this state.")
     End Sub
 End Class
Index: ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityStoppedState.vb
===================================================================
diff -u -r1735 -r1737
--- ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityStoppedState.vb	(.../ActivityStoppedState.vb)	(revision 1735)
+++ ActiviteitenOpvolging/ActiviteitenOpvolging/domain/classes/implementations/activity state/ActivityStoppedState.vb	(.../ActivityStoppedState.vb)	(revision 1737)
@@ -25,6 +25,10 @@
 
     ''' <inheritdoc/>
     Public Overrides Sub StartActivity(employee As IEmployee)
+        If IsNothing(employee) Then
+            'Nothing employee.
+            Throw New Exception($"The employee can't be nothing when starting an activity from stopped state.")
+        End If
         'Update employee.
         employee.CurrentActivity = me.Activity
         'Everyone can start this activity.