Exception handling in Spring to align with Front-End - spring

Question

Gone through the link https://www.mkyong.com/spring-boot/spring-boot-ajax-example/
and observed the following
Don't type any name and hit search button - Bad Request - It Comes to Error Function of Ajax - User Can't be Empty - Form Validation. Ajax response is error in this case.
Type "Raju" in name field and hit search button - Business Error - Returned with Success Function. Ajax response is success in this case.
Assume i have thrown a run time exception in getSearchResultViaAjax() as below
AjaxResponseBody result = new AjaxResponseBody();
if(1==1) {
throw new RuntimeException();
}
The same Ajax error block is getting called.
error: function (e) {
var json = "<h4>Ajax Response Error </h4><pre>"
+ e.responseText + "</pre>";
$('#feedback').html(json);
console.log("ERROR pp : ", e);
$("#btn-search").prop("disabled", false);
}
So for Bad Request and Any Exception which comes Out side the box comes in error block
Which would be the right approach in the following ? If both of them is incorrect, help me with the best practice
Approach One
Throw form validation errors as as Ajax Response is ERROR with failure message to display
Throw Business validation errors as Ajax Response is SUCCESS with failure message to display
Throw any other exception as Ajax Response is ERROR with failure message to display
OR
Approach Two
Throw form validation error as Ajax Response is ERROR with failure message to display ('User Field is Empty')
Throw Business validation errors as Ajax Response is FAILURE with failure message to display ('User Name doesn't exist')
Throw any other exception as Ajax Response is ERROR with failure message to display
What would be the best approach or best practice ?