Build error - can't find shared code

My client pages (apps) previously shared code via a directory in the workspace called "common" which I previously added to app.classpath in app/sencha.cfg. I've since moved this to app.json:

Code:

"classpath": "${app.dir}/app, ${workspace.dir}/common"

This seems to be recognized based on the build output:

Code:

[INF] Loading classpath entry /Users/paulb/Projects/BlueSage/LendingPlatform/web-app/lp/ /Users/paulb/Projects/BlueSage/LendingPlatform/web-app/common

but I'm getting an error:

Code:

[ERR] C2008: Requirement had no matching files (Common.ux.printer.HtmlRenderer) -- /Users/paulb/Projects/BlueSage/LendingPlatform/web-app/lp/app/application.js:923:10
[ERR] 
[ERR] BUILD FAILED
[ERR] com.sencha.exceptions.ExBuild: Failed to find any files for /Users/paulb/Projects/BlueSage/LendingPlatform/web-app/lp/app/application.js::ClassRequire::Common.ux.printer.HtmlRenderer
[ERR] 
[ERR] Total time: 4 seconds

That class is specified in the "requires" of my application.js like this:

Code:

requires: [
        'Common.ux.printer.HtmlRenderer'
]

This worked in previous versions. Am I doing something wrong?