Gradle how to include files conditionally?

Gradle: how to include different files conditionally?

For example,

file1.js
file2.js

file3.js
file4.js

from (zipTree("/foo/bar.jar")) {
   include {
       if (project.hasProperty("debug"))
          //file1.js, file2.js
       else
          //file3.js, file4.js
   }


}