code: @Nonnull
    public PreprocessorContext setSources(@Nonnull @MustNotContainNull final List<String> folderPaths) {
      this.sources.clear();
      this.sources.addAll(assertDoesntContainNull(folderPaths).stream().map(x -> new SourceFolder(this.baseDir, x)).collect(Collectors.toList()));
      return this;
    }
docs: Set source directories
  
  @param folderPaths list of source folder paths represented as strings
  @return this preprocessor context instance