fix: upload field validation not required (#1025)

src/fields/validations.ts

@@ -235,7 +235,7 @@ export const upload: Validate<unknown, unknown, UploadField> = (value: string, o
     return defaultMessage;
   }
 
-  if (!canUseDOM) {
+  if (!canUseDOM && typeof value !== 'undefined') {
     const idField = options.payload.collections[options.relationTo].config.fields.find((field) => fieldAffectsData(field) && field.name === 'id');
     const type = getIDType(idField);