How to use the krl-stdlib/types.isNull function in krl-stdlib

var delPVar = function(ldb, key_prefix, query, callback){
    var path = ktypes.isNull(query) ? [] : toKeyPath(query);
    if(_.size(path) > 0){
        key_prefix = key_prefix.concat(["value", _.head(path)]);
        var sub_path = _.tail(path);
        if( ! _.isEmpty(sub_path)){
            ldb.get(key_prefix, function(err, data){
                if(err && err.notFound){
                    data = {};
                }else if(err){
                    callback(err);
                    return;
                }
                var val = _.omit(data, sub_path);
                if(_.isEmpty(val)){
                    ldb.del(key_prefix, callback);
                }else{
                    ldb.put(key_prefix, val, callback);

var cleanQueryRules = function(rules){
    if(ktypes.isNull(rules)){
        return [];
    }
    if( ! _.isArray(rules)){
        throw new Error("`policy.query.` must be an Array of rules");
    }
    return _.map(rules, function(rule_orig){
        if( ! ktypes.isMap(rule_orig)){
            throw new Error("Policy rules must be Maps, not " + ktypes.typeOf(rule_orig));
        }
        assertOnlyAllowedProperties("Policy.query rule", rule_orig, ["rid", "name"]);

        var rule = {};
        if(!isBlank(rule_orig.rid)){
            rule.rid = rule_orig.rid.trim();
        }
        if(!isBlank(rule_orig.name)){

var fixLowerUpperArgs = function(args){
    return {
        lower: ktypes.isNull(args.lower)
            ? 1
            : _.parseInt(args.lower, 10) || 0,

        upper: ktypes.isNull(args.upper)
            ? 0
            : _.parseInt(args.upper, 10) || 0
    };
};

get: function (ctx, id) {
      var key = ctx.getMyKey(id)
      if (ktypes.isNull(key)) {
        throw new Error('keys:' + id + ' not defined')
      }
      return key
    }
  }

var cleanEventRules = function(rules){
    if(ktypes.isNull(rules)){
        return [];
    }
    if( ! _.isArray(rules)){
        throw new Error("`policy.event.` must be an Array of rules");
    }
    return _.map(rules, function(rule_orig){
        if( ! ktypes.isMap(rule_orig)){
            throw new Error("Policy rules must be Maps, not " + ktypes.typeOf(rule_orig));
        }
        assertOnlyAllowedProperties("Policy.event rule", rule_orig, ["domain", "type"]);

        var rule = {};
        if(!isBlank(rule_orig.domain)){
            rule.domain = rule_orig.domain.trim();
        }
        if(!isBlank(rule_orig.type)){

var fixLowerUpperArgs = function(args){
    return {
        lower: ktypes.isNull(args.lower)
            ? 1
            : _.parseInt(args.lower, 10) || 0,

        upper: ktypes.isNull(args.upper)
            ? 0
            : _.parseInt(args.upper, 10) || 0
    };
};