code: protected Collection<GrantedAuthority> transformToSimpleAuthorities(Set<String> strAuthorities, boolean appendRolePrefix) {
  		if (null != strAuthorities) {
  			Collection<GrantedAuthority> authorities = new HashSet<>(strAuthorities.size());
  			for (String authority : strAuthorities) {
  				if (!StringUtils.isEmpty(authority)) {
  					String role = authority.trim().toUpperCase(Locale.ENGLISH);
  					if (appendRolePrefix) {
  						authorities.add(new SimpleGrantedAuthority(getRolePrefix() + role));
  					} else {
  						authorities.add(new SimpleGrantedAuthority(role));
  					}
  				}
  			}
  			return authorities;
  		}
  		return Collections.emptyList();
  	}
docs: transforms all authorities to upper case and append the prefix if appendRolePrefix = true
  
  @param strAuthorities
  @param appendRolePrefix
  @return Empty collection or collection of {@link SimpleGrantedAuthority}