code: protected void checkRepositoryMapIsValid(File repositoryMap) throws MojoExecutionException {
          URL schemaFile = this.getClass().getResource("/RepositoryMap.xsd");
          Source xmlFile = new StreamSource(repositoryMap);
          SchemaFactory schemaFactory = SchemaFactory.newInstance(XMLConstants.W3C_XML_SCHEMA_NS_URI);
          try {
              Schema schema = schemaFactory.newSchema(schemaFile);
              Validator validator = schema.newValidator();
              validator.validate(xmlFile);
              LOG.info("Repository map '" + xmlFile.getSystemId() + "' is valid");
              LOG.info(" ");
          } catch (SAXException | IOException ex) {
              throw new MojoExecutionException(repositoryMap.getName() + " is not valid: " + ex.getLocalizedMessage());
          }
      }
docs: Validate any custom repository maps that are supplied against the xsd.
  Throw an error and stop if it is not valid.
  Assume it doesn't exist if we get an IOError and fall back to default file.
  
  @throws MojoExecutionException thrown if customRepositoryMap is not valid