omit email if not entered

aleksis/apps/paweljong/frontend/components/event_registration/EventRegistrationForm.vue

@@ -736,7 +736,7 @@ import SecondaryActionButton from "aleksis.core/components/generic/buttons/Secon
       dataForSubmit() {
         const { confirmEmail, confirmPassword, ...filteredUserData } = this.data.user;
 
-        const data = {
+        let data = {
           ...this.data,
           additionalFields: JSON.stringify(this.data.additionalFields),
           terms: JSON.stringify(this.data.terms),
@@ -745,7 +745,11 @@ import SecondaryActionButton from "aleksis.core/components/generic/buttons/Secon
 
         if (this.event.cost == 0 && this.event.maxCost == 0) {
           const { payment, ...filteredData } = data;
-          return filteredData;
+          data = filteredData;
+        }
+        if (!this.data.email.localPart && !this.data.email.domain) {
+          const { email, ...filteredData } = data;
+          data = filteredData;
         }
         return data;
       },