Why is this "${varname}:?}" not flaged as an error

I stumbled upon this error introduced by my inapt fat fingers in a bash script:
`
function f {
    local v="${1}:?}"
    ...
}
`

What I clearly meant was this:
`
function f {
    local v="${1:?}"
    ...
}
`

But the extra, erroneous "}" in the local variable definition was not indicated by this otherwise excelent ShellCheck thingie.

