Pipeline with XSLT soap output, how to submit to web service?

adam_gataev - you were very close - try this

.map((elem, idx, arr) =>
    {
        "fieldA": elem.fieldA,
        "fieldB": [
            {
                "fieldC1": elem.fieldC1,
                "fieldC2": elem.fieldC2
            }
        ]
        .concat(
	       elem.get('fieldD1') > ''
	       ? [
   	            {
                    "fieldD1": elem.fieldD1,
                    "fieldD2": elem.fieldD2
                }
	        ] 
	       : []
        )
        .concat(
           elem.get('fieldE1') > ''
	       ? [
                {
                    "fieldE1": elem.fieldE1,
                    "fieldE2": elem.fieldE2
                }
             ] 
	        : []
    )
    }
)

Hope this helps!