code: public Iterable<? extends File> getClassPath(File root, Iterable<? extends File> classPath) {
          return this.classPath == null
                  ? new PrefixIterable(root, classPath)
                  : this.classPath;
      }
docs: Returns the class path or builds a class path from the supplied arguments if no class path was set.
  
  @param root      The root directory of the project being built.
  @param classPath The class path dependencies.
  @return An iterable of all elements of the class path to be used.