code: private List<RuleSource> readRulesDirectory(File rulesDirectory) throws MojoExecutionException {
          if (rulesDirectory.exists() && !rulesDirectory.isDirectory()) {
              throw new MojoExecutionException(rulesDirectory.getAbsolutePath() + " does not exist or is not a directory.");
          }
          getLog().info("Reading rules from directory " + rulesDirectory.getAbsolutePath());
          try {
              return FileRuleSource.getRuleSources(rulesDirectory);
          } catch (IOException e) {
              throw new MojoExecutionException("Cannot read rulesDirectory: " + rulesDirectory.getAbsolutePath(), e);
          }
      }
docs: Retrieves the list of available rules from the rules directory.
  
  @param rulesDirectory The rules directory.
  @return The {@link java.util.List} of available rules
  {@link java.io.File}s.
  @throws MojoExecutionException If the rules directory cannot be read.