not tested but try this:
{{get(first(map(yourarray; if(get(item; "key") = ""; get(item; "values"; emptyarray); emptyarray))); 0)}}
Iterator:
{{get(first(map(yourarray; if(get(item; "key") = {2.value}; get(item; "values"; emptyarray); emptyarray))); 0)}}