Error: Cannot read property 'toLowerCase' of undefined

[marcoconti83]

I'm on macOS 10.12.4.

If I create a file with this content:

print 42

and save it as "do.swift", then from the menu "Debug" -> "Start debug", I get an error:

Cannot read property 'toLowerCase' of undefined

This is the content of my settings:

// Place your settings in this file to overwrite the default settings
{
    "swift.path.sourcekite": "/Users/marcoconti/DEV/sourcekite/.build/debug/sourcekite"
}

[johndpope]

this is happening on mac / xcode 8.3 + sierra latest. all system updated.