Preparing a rendered exr with multiple render layers

I'm a complete newb to this so please bear with me. I want to automate the process of preparing rendered exr's

I used the script listener to create what I need to do, however, some of my files have variables.

For example, i may be supplied with i file that doesn't have certain elements in it, this obviously breaks the script.

The example here shows that the file has layers called "multimatte.RGB" sometimes I have 1, the example bellow selects 3 layers but sometimes i don't have any layers named this. How do i get it to work as an if?

var idslct = charIDToTypeID( "slct" );

    var desc179 = new ActionDescriptor();

    var idnull = charIDToTypeID( "null" );

        var ref163 = new ActionReference();

        var idLyr = charIDToTypeID( "Lyr " );

        ref163.putName( idLyr, "multimatte.RGB" );

    desc179.putReference( idnull, ref163 );

    var idMkVs = charIDToTypeID( "MkVs" );

    desc179.putBoolean( idMkVs, false );

executeAction( idslct, desc179, DialogModes.NO );

// =======================================================

var idslct = charIDToTypeID( "slct" );

    var desc180 = new ActionDescriptor();

    var idnull = charIDToTypeID( "null" );

        var ref164 = new ActionReference();

        var idLyr = charIDToTypeID( "Lyr " );

        ref164.putName( idLyr, "multimatte2.RGB" );

    desc180.putReference( idnull, ref164 );

    var idselectionModifier = stringIDToTypeID( "selectionModifier" );

    var idselectionModifierType = stringIDToTypeID( "selectionModifierType" );

    var idaddToSelectionContinuous = stringIDToTypeID( "addToSelectionContinuous" );

    desc180.putEnumerated( idselectionModifier, idselectionModifierType, idaddToSelectionContinuous );

    var idMkVs = charIDToTypeID( "MkVs" );

    desc180.putBoolean( idMkVs, false );

executeAction( idslct, desc180, DialogModes.NO );

Thanks