(nested subsector) queries fail using rgcam

[mbins]

rgcam often fails when running queries from GCAM's Main_queries.xml with (nested subsector) in the query name. The issue appears to stem from the fact that these queries use variable depth of subsector nesting in a single query (indicated by the the // between subsector & technology, as in the example below).

            <emissionsQueryBuilder title="CO2 emissions by tech (nested subsector) (excluding resource production)">
                <axis1 name="technology">technology</axis1>
                <axis2 name="Year">emissions</axis2>
                <xPath buildList="true" dataName="emissions" group="false" sumAll="false">*[@type = 'sector' ]/*[@type='subsector']//*[@type='technology']//
            CO2/emissions/node()</xPath>
                <comments/>
            </emissionsQueryBuilder>

A workaround is to split the query in two - one with standard sector/subsector/technology structure, and another that specifies the depth of subsector nesting (note that this requires knowing the number of nesting subsectors in the sectors the query is targeting) - in order to extract the info for nested and non-nested subsectors, which can then be recombined.
example of query for standard sector/subsector/technology structure (note that the structure is *[@type='subsector']/ instead of *[@type='subsector']//:

            <emissionsQueryBuilder title="CO2 emissions by tech (excluding resource production)">
                <axis1 name="technology">technology</axis1>
                <axis2 name="Year">emissions</axis2>
                <xPath buildList="true" dataName="emissions" group="false" sumAll="false">*[@type = 'sector' ]/*[@type='subsector']/*[@type='technology']//
            CO2/emissions/node()</xPath>
                <comments/>
            </emissionsQueryBuilder>

example of query for one nested subsector (2 subsectors in total; note that *[@type='subsector']/ is repeated twice):

        <queryGroup name="CO2 emissions">
            <emissionsQueryBuilder title="CO2 emissions by tech (nested subsector) (excluding resource production)">
                <axis1 name="technology">technology</axis1>
                <axis2 name="Year">emissions</axis2>
                <xPath buildList="true" dataName="emissions" group="false" sumAll="false">*[@type = 'sector' ]/*[@type='subsector']/*[@type='subsector']/*[@type='technology']//
            CO2/emissions/node()</xPath>
                <comments/>
            </emissionsQueryBuilder>