code: private List<JqassistantRules> readXmlSource(RuleSource ruleSource) {
          List<JqassistantRules> rules = new ArrayList<>();
          try (InputStream inputStream = ruleSource.getInputStream()) {
              JqassistantRules jqassistantRules = jaxbUnmarshaller.unmarshal(inputStream);
              rules.add(jqassistantRules);
          } catch (IOException e) {
              throw new IllegalArgumentException("Cannot read rules from '" + ruleSource.getId() + "'.", e);
          }
          return rules;
      }
docs: Read rules from XML documents.
  
  @param ruleSource
  The available sources.
  @return The list of found rules.