Springframework custom nested tag issue

I am trying to create a custom XSD based configuration. I have custom tag which has another custom tag in turn. When parsing the inner tag, I get namespace handler not found. It could not locate handler class for http://ift.tt/GArMu6 schema.

Sample XML:

<beans xmlns="http://ift.tt/GArMu6"
    xmlns:xsi="http://ift.tt/ra1lAU" 
    xmlns:or="http://ift.tt/1BuRdW2"
    xsi:schemaLocation="http://ift.tt/GArMu6 http://ift.tt/1cnl1uo
    http://ift.tt/1Cu8JPd http://ift.tt/1Cu8Lqj">

    <or:springRestTemplate id="customTemplateTest" >
        <or:basicAuth id="templateCreds" userName="restUser" password="restPassword" />
        <or:httpHeaders >
            <map>
                <entry key="headerName" value="headerValue" />
            </map>
        </or:httpHeaders>
    </or:springRestTemplate>

</beans>

Parser code:

@Override
    protected AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
        BeanDefinitionBuilder restTemplate = BeanDefinitionBuilder.rootBeanDefinition(SpringRestTemplateWithInterceptorsFactoryBean.class);

        List<Element> credentials = DomUtils.getChildElementsByTagName(element, AUTH_CHILD_ELEMENT);
        if (credentials != null && !credentials.isEmpty()) {
            restTemplate.addPropertyValue("basicAuth", parserContext.getDelegate().parseCustomElement(credentials.get(0)));
        }

        List<Element> httpHeadersElements = DomUtils.getChildElementsByTagName(element, HTTP_HEADER_CHILD_ELEMENT);
        if (httpHeadersElements != null && !httpHeadersElements.isEmpty()) {
            httpHeadersElements = DomUtils.getChildElementsByTagName(httpHeadersElements.get(0), "map");
        }

        if (httpHeadersElements != null && !httpHeadersElements.isEmpty()) {
            restTemplate.addPropertyValue("httpHeaders", parserContext.getDelegate().parseCustomElement(httpHeadersElements.get(0)));
        }

        return restTemplate.getBeanDefinition();
    }

I get error on this line:

restTemplate.addPropertyValue("httpHeaders", parserContext.getDelegate().parseCustomElement(httpHeadersElements.get(0)));

I tried to debug the issue. I see that parserContext has all Spring schema handlers loaded, expect for the beans schema.