Added import validation message when no "Email" mapping selected

no issue

- Ensures the "email" field required to create a member is always present with the mapping
- If the field is not mapped, import would fail for all members

ghost/admin/app/components/modal-import-members.hbs

@@ -51,6 +51,27 @@
         {{/if}}
 
         {{#if this.customizing}}
+            {{#if this.uploadErrors}}
+                <div class="failed flex items-start gh-members-upload-errorcontainer {{if this.importDisabled "error" "warning"}}">
+                    <div class="mr3">
+                        {{svg-jar "warning" class="nudge-top--2 w5 h5 fill-red"}}
+                    </div>
+                    <div class="ma0">
+                        <p class="ma0 pa0 flex-grow w-100">The import contains errors!</p>
+                        <ul class="ma0 pa0 mt4 list bt b--whitegrey">
+                            {{#each this.uploadErrors as |error|}}
+                                <li class="gh-members-import-errormessage">
+                                    <span>{{{error.message}}}</span>
+                                    {{#if error.context}}
+                                        <p class="gh-members-import-errorcontext">{{{error.context}}}</p>
+                                    {{/if}}
+                                </li>
+                            {{/each}}
+                        </ul>
+                    </div>
+                </div>
+            {{/if}}
+
             <GhFormGroup>
                 {{#if this.config.enableDeveloperExperiments}}
                     <div class="gh-members-import-scrollarea">

ghost/admin/app/components/modal-import-members.js

@@ -41,6 +41,16 @@ class MembersFieldMapping {
         return this._mapping;
     }
 
+    getKeyByValue(searchedValue) {
+        for (const [key, value] of Object.entries(this._mapping)) {
+            if (value === searchedValue) {
+                return key;
+            }
+        }
+
+        return null;
+    }
+
     updateMapping(from, to) {
         for (const key in this._mapping) {
             if (this.get(key) === to) {
@@ -75,6 +85,7 @@ export default ModalComponent.extend({
     importResponse: null,
     failureMessage: null,
     validationErrors: null,
+    uploadErrors: null,
     labels: null,
 
     // Allowed actions
@@ -189,6 +200,7 @@ export default ModalComponent.extend({
             this.set('fileData', null);
             this.set('mapping', null);
             this.set('validationErrors', null);
+            this.set('uploadErrors', null);
 
             this.set('validating', false);
             this.set('customizing', false);
@@ -197,8 +209,13 @@ export default ModalComponent.extend({
         },
 
         upload() {
-            if (this.file) {
+            if (this.file && this.mapping.getKeyByValue('email')) {
                 this.generateRequest();
+            } else {
+                this.set('uploadErrors', [{
+                    message: 'Import as "Email" value is missing.',
+                    context: 'The CSV has to contain import as "Email" field.'
+                }]);
             }
         },