code: private String makeConverterKey(Class<?> fromClass, String syntax, Class<?> toClass) {
          StringBuilder key = new StringBuilder();
          if (syntax==null) {
              syntax="";
          }
          key.append(fromClass.getName()).append(KEY_SEP).append(syntax).append(KEY_SEP).append(toClass.getName());
          return key.toString();
      }
docs: Make a key into the converters map - the keys is formed from the <code>fromClass</code>, syntax and <code>toClass</code>
  
  @param fromClass The class to convert from.
  @param syntax The LDAP syntax.
  @param toClass The class to convert to.
  @return key