expected_two_map_type_arguments

Map literals require two type arguments or none, but {0} found.

The analyzer produces this diagnostic when a map literal has either one or more than two type arguments.

The following code produces this diagnostic because the map literal has three type arguments when it can have either two or zero:

var m = <int, String, int>{};

Remove all except two of the type arguments:

var m = <int, String>{};