Remove empty payload from GET requests

[edgars-vasiljevs]

Currently all Inertia GET requests have Content-Type: application/json header applied because empty object is passed as a payload. Axios sees an object and sets content type to application/json even though request body is empty.

This is an issue because Laravel interprets these requests differently than regular GET request. See here

One example where this is a problem - for example I have GET route and I want to add or update some query parameters in current request using request()->merge(['foo' => 'bar'])

When running request()->query() I expect to get foo parameter back since it is a GET request. Instead I get nothing. This is because merge runs on json input source instead of query. See here and here

Setting data to null is enough for Axios to ignore payload.

[edgars-vasiljevs]

Here is another case

->get(..) method is broken on any request instance derived from original request.

$request = Request::createFrom(request());

request()->merge(['foo1' => 'bar']);
$request->merge(['foo2' => 'bar']);

var_export(request()->get('foo1'));
var_export($request->get('foo2'));

// GET request without content-type "application/json" header
'bar'
'bar'

// GET request with content-type "application/json" header
'bar'
NULL

For example this breaks spatie/laravel-query-builder package since it uses ->get() method internally to get filter/sorting params from query.