json syntax error on page save in AdminController

Trying to set up user specific editing rights on a page
Allows setting inherit permissions true
and page authors to username
crashes when attempting to set any group value
arguments coming in to AdminController are
```
array:11 [[▼]()
"header" => array:6 [[▼]()
"title" => "test"
"media_order" => ""
"body_classes" => ""
"order_by" => ""
"order_manual" => ""
"permissions" => array:1 [[▼]()
"authors" => array:1 [[▼]()
0 => "andyf"
]
]
]
"content" => "test page"
"folder" => "test"
"route" => "/dashboard/exchange"
"name" => "default"
"ordering" => "0"
"order" => ""
"order-child" => ""
"blueprint" => "foo"
"_json" => array:1 [[▼]()
"header" => array:1 [[▼]()
"permissions" => array:1 [[▼]()
"groups" => array:2 [[▼]()
"internal" => "{"create":"1","read":"1","update":"1","delete":"1"}"
0 => array:1 [[▼]()
"dashboard/exchange/test" => ""
]
]
]
]
]
"lang" => ""
```