Http 400 Error Submitting a Form With Errors With Spring

So I got a http 400 error when testing a form I thought used to work.
Something like this

I’m using Spring MVC.
The form will submit fine if there are no errors but fails with a 400 error if there’s a validation problem.

It’s likely the curse of the evil copy and paste.

@RequestMapping(method = RequestMethod.POST, value = "/something")  
    public String somethingPost(Model model, @Valid SomeForm form,   
            HttpServletRequest req, BindingResult result) {  

So it looks harmless enough but it should look like this

@RequestMapping(method = RequestMethod.POST, value = "/something")  
    public String somethingPost(Model model, @Valid SomeForm form,   
            BindingResult result, HttpServletRequest req) {  

The Binding result must follow the form, I had pasted HttpServletRequest req in between them and borked the binding.

http://docs.spring.io/spring/docs/4.1.x/spring-framework-reference/html/mvc.html#mvc-ann-methods

org.springframework.validation.Errors / org.springframework.validation.BindingResult validation results for a preceding command or form object (the immediately preceding method argument).