private static X509KeyManager getDefaultX509KeyManager() throws KeyManagementException {
        X509KeyManager result = defaultX509KeyManager;
        if (result == null) {
            // single-check idiom
            defaultX509KeyManager = result = createDefaultX509KeyManager();
        }
        return result;
    }
Returns X.509 key manager or null for none.
common/src/main/java/org/conscrypt/SSLParametersImpl.java