private static String toHexString(long subqueryBitMap) {
        return "0x" + Long.toHexString(subqueryBitMap);
    }
Converts {@link PredicateQuery} to and from JSON

Example:
 {
     features: [
         {"k": "key-name", "v":"value", "s":"0xDEADBEEFDEADBEEF"}
     ],
     rangeFeatures: [
         {"k": "key-name", "v":42, "s":"0xDEADBEEFDEADBEEF"}
     ]
 }

@author bjorncs
predicate-search/src/main/java/com/yahoo/search/predicate/serialization/PredicateQuerySerializer.java