Service Desk SLA Custom Field values are excluded in XML format

Issue Summary

When user search any issue from Issue Navigator, they can see the Time waiting for support and Time to resolution values as per issue-navi.png screenshot.
Export issues to Excel also able to show the Time waiting for support and Time to resolution values as per xls.png screenshot.
However, the data is not shown in XML format as per xml2.png screenshot.

Steps to Reproduce

1. Have some issues with SLA
2. Export to XML format

Expected Results

The exported XML file doesn't contain SLA values

<customfield id="customfield_15111" key="com.atlassian.servicedesk:sd-sla-field">
<customfieldname>Time to approve normal change</customfieldname>
<customfieldvalues> </customfieldvalues>
</customfield>

Actual Results

It should show the SLA value just as when we export to CSV/excel

Workaround

Export to CSV format