public boolean hasSource(String name) {
        if (sources.isEmpty() && name.equals(getName())) {
            return true;
        }
        for (Source s : sources) {
            if (s.getName().equals(name)) {
                return true;
            }
        }
        return false;
    }
Returns a summary field which merges the settings in the given field
into this field

@param  merge the field to merge with this, if null, the merged field is *this* field
@throws RuntimeException if the two fields can not be merged
config-model/src/main/java/com/yahoo/vespa/documentmodel/SummaryField.java