What you're trying to do is something called "volumetric CBC," not "chip allocation". In chip allocation, we usually think of having a constant number of chips to allocate in each choice task.
But, it would be strange to ask respondents to specify how much volume they'd purchase across multiple alternatives and then also to include a None option. Usually, you do not include a "None" option for the design of the questionnaire and for the fielding of the questions.
There are multiple ways to analyze the results, the more sophisticated methods are described by Tom Eagle in a 2010 Sawtooth Software Conference Proceedings article.
A relatively simple approach that can work quite well for straightforward CBC datasets (assuming respondents can actually do volumetric CBC questionnaires well, which is totally up for debate) is to field a CBC questionnaire allowing respondents to type values for each alternative. Do not include a None in the fielding of the questionnaire.
But, on the back end, you modify the CBC design to "trick" CBC software into thinking that a None concept was included in each choice task. For each respondent, scan across the tasks to find the largest total volume "purchased" of product within that task. Let's say for your study respondent #1 bought 20 products in one of the choice tasks (and that was equal to their max purchased across all choice tasks). For that choice task, the None alternative gets "0" chips. But, for another choice task for Resp#1 where the respondent only "purchased" 10 units, a full 10 chips is assigned to the None. You can export the .CSV file including the Raw CBC data and make modifications to it to accomplish this.
Then, proceed with HB estimation as usual using our software (running CBC/HB standalone software on the modified .CSV file). But, in the market simulator, you must weight each respondent by the maximum number of purchases the respondent made across their choice tasks. For example, above, Resp#1 would be weighted by "20".