make_model: be aware of array with empyt slots

src/util/make_model.js

@@ -61,11 +61,8 @@ export default (options={}) => {
 				limit = _cache.upstream_limit || _cache.count || Infinity
 
 			// be lazy 1: if the data is presented, return the value immediately
-			//
-			// note that Array.every(list) == true if list is empty
-			let _portion = _cache.data.slice(offset, offset+limit)
-			if (_portion.length > 0 && _portion.every(data => data != undefined))
-				return Promise.resolve(_portion)
+			if (this.data(offset, limit).length > 0 && !this.data(offset, limit).includes(undefined))
+				return Promise.resolve(this.data(offset, limit))
 
 			// be lazy 2: if there is a promise, return it if ambient matches or
 			// cancel it