@Nullable
    private static String toScopeString(@Nullable List<String> scopeList) {
        if (scopeList == null || scopeList.isEmpty()) {
            return null;
        }
        return String.join(SCOPE_SEPARATOR, scopeList);
    }
{@code JSON}-formatted raw Token Introspection Response body. If the {@link GrantedOAuth2AccessToken} was
not parsed out of the raw response body, this value calculated based on the other
{@link GrantedOAuth2AccessToken} values.
oauth2/src/main/java/com/linecorp/armeria/common/auth/oauth2/GrantedOAuth2AccessToken.java