protected void setAuthenticatorIfUndefined(final Authenticator authenticator) {
        if (this.authenticator == null) {
            this.authenticator = authenticator;
        }
    }
<p>setAuthenticatorIfUndefined.</p>

@param authenticator a {@link Authenticator} object
pac4j-core/src/main/java/org/pac4j/core/client/BaseClient.java