relationships: make sort field null if empty (#9735)

app/src/modules/settings/routes/data-model/field-detail/field-detail-advanced/field-detail-advanced-relationship-m2a.vue

@@ -62,7 +62,12 @@
 
 		<div class="sort-field">
 			<v-divider large :inline-title="false">{{ t('sort_field') }}</v-divider>
-			<related-field-select v-model="sortField" :collection="junctionCollection" :placeholder="t('add_sort_field')" />
+			<related-field-select
+				v-model="sortField"
+				:collection="junctionCollection"
+				:placeholder="t('add_sort_field')"
+				:nullable="true"
+			/>
 		</div>
 
 		<div class="relational-triggers">

app/src/modules/settings/routes/data-model/field-detail/field-detail-advanced/field-detail-advanced-relationship-m2m.vue

@@ -72,6 +72,7 @@
 				v-model="sortField"
 				:collection="junctionCollection"
 				:placeholder="t('add_sort_field') + '...'"
+				:nullable="true"
 			/>
 		</div>
 

app/src/modules/settings/routes/data-model/field-detail/field-detail-advanced/field-detail-advanced-relationship-o2m.vue

@@ -25,6 +25,7 @@
 				v-model="sortField"
 				:collection="relatedCollection"
 				:placeholder="t('add_sort_field') + '...'"
+				:nullable="true"
 			/>
 		</div>
 

app/src/modules/settings/routes/data-model/field-detail/shared/related-field-select.vue

@@ -2,11 +2,11 @@
 	<v-input
 		:model-value="modelValue"
 		db-safe
-		:nullable="false"
+		:nullable="nullable"
 		:disabled="disabled"
 		:placeholder="placeholder"
 		:class="{ matches: fieldExists }"
-		@update:model-value="$emit('update:modelValue', $event)"
+		@update:model-value="$emit('update:modelValue', $event.length ? $event : null)"
 	>
 		<template v-if="fields && fields.length > 0 && !disabled" #append>
 			<v-menu show-arrow placement="bottom-end">
@@ -65,6 +65,10 @@ export default defineComponent({
 			type: String,
 			default: () => i18n.global.t('foreign_key') + '...',
 		},
+		nullable: {
+			type: Boolean,
+			default: false,
+		},
 	},
 	emits: ['update:modelValue'],
 	setup(props) {