Merge pull request #90 from moosetechnology/89-improve-error-reportin…

…g-when-there-is-an-issue-with-fame-slots

Catching the SlotNotFound error and added a comment to help users debug

src/Fame-Core/FMRelationSlot.class.st

@@ -50,7 +50,19 @@ FMRelationSlot >> addAssociationFrom: ownerObject to: otherObject [
 	association may have to be removed first."
 
 	| realInverseSlot |
-	realInverseSlot := self realInverseSlotFor: otherObject.
+
+	[
+		realInverseSlot := self realInverseSlotFor: otherObject
+	] on: SlotNotFound
+	do: [ :err |
+		"The reverse slot was not found.
+		 To investigate the problem, inspect:
+		 - ownerObject -- The object which relation is set
+		 - otherObject == The object which is set in the relation
+		 - `self name` -- The name of the relation in ownerObject that is set to otherObject
+		 - `self targetClass` -- The expected type for otherObject"
+		self halt.
+	].
 
 	realInverseSlot isToOne
 		ifTrue: [ (realInverseSlot read: otherObject) ifNotNil: [ :oldObject | realInverseSlot removeAssociationFrom: otherObject to: oldObject ].