Declare as INodeProperties instead of casting

credentials/FriendGridApi.credentials.ts

@@ -1,21 +1,21 @@
 import {
 	ICredentialType,
-	NodePropertyTypes,
+	INodeProperties,
 } from 'n8n-workflow';
 
 export class FriendGridApi implements ICredentialType {
 	name = 'friendGridApi';
 	displayName = 'FriendGrid API';
 	documentationUrl = 'friendGrid';
-	properties = [
+	properties: INodeProperties[] = [
 		// The credentials to get from user and save encrypted.
 		// Properties can be defined exactly in the same way
 		// as node properties.
 		{
 			displayName: 'API Key',
 			name: 'apiKey',
-			type: 'string' as NodePropertyTypes,
+			type: 'string',
 			default: '',
 		},
 	];
-}
+}