Throw an error when there are multiple components to render the same type/viewmode combination

src/app/shared/entities/relationship-type-decorator.ts

-import { hasNoValue } from '../empty.util';
+import { hasNoValue, hasValue } from '../empty.util';
 import { ElementViewMode } from '../view-mode';
 
 export const DEFAULT_RELATIONSHIP_TYPE = 'Default';
@@ -9,6 +9,9 @@ export function rendersRelationshipType(type: string, viewMode: ElementViewMode)
     if (hasNoValue(map.get(viewMode))) {
       map.set(viewMode, new Map());
     }
+    if (hasValue(map.get(viewMode).get(type))) {
+      throw new Error(`There can't be more than one component to render Items of type "${type}" in view mode "${viewMode}"`);
+    }
     map.get(viewMode).set(type, component);
   };
 }