diff --git a/lib/contracts/contracts.ts b/lib/contracts/contracts.ts
index ce88d028..02507667 100644
--- a/lib/contracts/contracts.ts
+++ b/lib/contracts/contracts.ts
@@ -67,7 +67,7 @@ export namespace Contracts {
         name: string;
         type: string;
         value: any;
-        taxonomy_group?: string;
+        taxonomy_group: string;
     }
 
     export interface IDateTimeElementContract extends IElementContract {
diff --git a/lib/mappers/element.mapper.ts b/lib/mappers/element.mapper.ts
index 7351ebe8..d0a8700a 100644
--- a/lib/mappers/element.mapper.ts
+++ b/lib/mappers/element.mapper.ts
@@ -307,7 +307,7 @@ export class ElementMapper {
     private mapTaxonomyElement(elementWrapper: ElementModels.IElementWrapper): Elements.TaxonomyElement {
         return {
             ...this.buildElement(elementWrapper, ElementType.Taxonomy, () => elementWrapper.rawElement.value),
-            taxonomyGroup: elementWrapper.rawElement.taxonomy_group ?? null
+            taxonomyGroup: elementWrapper.rawElement.taxonomy_group
         };
     }