Publishing API's in WSO2 ESB using WSO2 API Manager - wso2

Question

I can't publish API's in WSO2 ESB from WSO2 API Manager. My legacy architecture has two WSO2 ESB instances, first ESB is only a Gateway component, and second ESB works conventionally.
Now, I need to use an API Manager instances to publish API's in the ESB's intances.
But, I configure APIGateway section in /repository/conf/api-manager.xml to point to ESB instance, like this:
<APIGateway>
<Environments>
<Environment type="production" api-console="true">
<Name>Production and Sandbox</Name>
<Description> Description of environment</Description>
<!--ServerURL>https://${carbon.local.ip}:${mgt.transport.https.port}${carbon.context}/services/</ServerURL-->
<ServerURL>https://localhost:8243/services/</ServerURL>
<!--Username>${admin.username}</Username-->
<Username>admin</Username>
<!--Password>${admin.password}</Password-->
<Password>admin</Password>
<!--GatewayEndpoint>http://${carbon.local.ip}:${http.nio.port},https://${carbon.local.ip}:${https.nio.port}</GatewayEndpoint-->
<GatewayEndpoint>http://localhost:8280,https://localhost:8243</GatewayEndpoint>
</Environment>
</Environments>
<EnableGatewayKeyCache>true</EnableGatewayKeyCache>
<EnableGatewayResourceCache>true</EnableGatewayResourceCache>
<ClientDomainHeader>referer</ClientDomainHeader>
</APIGateway>
And, in I tired to point to 8243 port as well, and I couldn't publish in ESB instance.
In logs, I can see following:
2016-05-05 08:33:29,551 [-] [http-nio-9443-exec-42] INFO LogMediator To: https://localhost:9443/services/APIGatewayAdmin, From: 127.0.0.1, WSAction: urn:getApi, SOAPAction: urn:getApi, Direction: request, Envelope: <?xml version='1.0' encoding='utf-8'?><soapenv:Envelope xmlns:soapenv="http://www.w3.org/2003/05/soap-envelope"><soapenv:Body><ns2:getApi xmlns:ns2="http://service.gateway.apimgt.carbon.wso2.org"><ns2:apiProviderName>admin</ns2:apiProviderName><ns2:apiName>name</ns2:apiName><ns2:version>1.0</ns2:version></ns2:getApi></soapenv:Body></soapenv:Envelope>
So, API Manager tries publish in ESB, and ESB recives request but I get only one error in logs a few lines below:
2016-05-05 08:33:55,865 [-] [http-nio-9443-exec-4] DEBUG AxisServlet
java.lang.NullPointerException
at javax.servlet.GenericServlet.getServletContext(GenericServlet.java:123)
at org.apache.axis2.transport.http.AxisServlet.createMessageContext(AxisServlet.java:715)
[...]
2016-05-05 08:33:55,867 [-] [http-nio-9443-exec-4] DEBUG Options getAction (null) from org.apache.axis2.client.Options#353f3a03
Do I need to configure the ESB to do this?