private List<File> scanSourceFiles() {
final List<File> asciidoctorFiles;
if (extensions == null || extensions.isEmpty()) {
final DirectoryWalker directoryWalker = new AsciiDocDirectoryWalker(sourceDirectory.getAbsolutePath());
asciidoctorFiles = directoryWalker.scan();
} else {
final DirectoryWalker directoryWalker = new CustomExtensionDirectoryWalker(sourceDirectory.getAbsolutePath(), extensions);
asciidoctorFiles = directoryWalker.scan();
}
String absoluteSourceDirectory = sourceDirectory.getAbsolutePath();