Typescript compiler error: Cannot call method 'toLowerCase' of undefined

I am convertng my NodeJs + ExpressJS project to Typescript, and I see this compiler error in the console. It does not even point at any specific code segment, which is why I don't know where to start diagnosing the problem. This project uses NodeJS + ExpressJS. I'm coding it in Webstorm and the Webstorm "FileWatcher" for Typescript automatically compiles the project.

C:/Users/Me/AppData/Roaming/npm/tsc.cmd --sourcemap Main.d.ts --out main.js --module

C:\Users\Me\AppData\Roaming\npm\node_modules\typescript\bin\tsc.js:55958
                    type = type.toLowerCase();
                                ^
TypeError: Cannot call method 'toLowerCase' of undefined
    at Object.opts.option.set (C:\Users\Me\AppData\Roaming\npm\node_modules\typescript\bin\tsc.js:55958:33)
    at OptionsParser.parse (C:\Users\Me\AppData\Roaming\npm\node_modules\typescript\bin\tsc.js:55506:36)
    at BatchCompiler.parseOptions (C:\Users\Me\AppData\Roaming\npm\node_modules\typescript\bin\tsc.js:56054:18)
    at BatchCompiler.batchCompile (C:\Users\Me\AppData\Roaming\npm\node_modules\typescript\bin\tsc.js:55576:22)
    at Object.<anonymous> (C:\Users\Me\AppData\Roaming\npm\node_modules\typescript\bin\tsc.js:56298:7)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.require (module.js:364:17)