default boolean hasNumericValue() {
        return false;
    }
@return True if the underlying value is non-null, has a numeric value,
e.g. "1", "1.2", 300, etc, or can be represented as a number, e.g. a date string
represented as millis since epoch.
stroom-query/stroom-query-language/src/main/java/stroom/query/language/functions/Val.java