pos fp fix

model.js

point_of_sale: [FIX] fp map to empty tax


Before this commit, `_map_tax_fiscal_position` could map to undifined, if the
target tax was empty (a valid use case, in other words: "remove").

This commit filters or validates the mapping result in order to take care of the
undifined returns. As it is construed as a mapping function, we cannot take
care within the function itself but must handle it in downstream code.

Alternatively a wrapper could be made to encapuslate this safety check as well.

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diff --git a/addons/point_of_sale/static/src/js/models.js b/addons/point_of_sale/static/src/js/models.js
index 3de8074..1450e83 100644
--- a/addons/point_of_sale/static/src/js/models.js
+++ b/addons/point_of_sale/static/src/js/models.js
@@ -1575,7 +1575,7 @@ exports.Orderline = Backbone.Model.extend({
                 return t.id === el;
             }));
         });
-        product_taxes = _.map(product_taxes, this._map_tax_fiscal_position.bind(this));
+        product_taxes = _.map(product_taxes, this._map_tax_fiscal_position.bind(this)).filter(function(x){return x != undefined});
 
         var all_taxes = this.compute_all(product_taxes, price_unit, this.get_quantity(), this.pos.currency.rounding);
         _(all_taxes.taxes).each(function(tax) {
@@ -2071,7 +2071,7 @@ exports.Order = Backbone.Model.extend({
             var mapped_included_taxes = [];
             _(taxes).each(function(tax) {
                 var line_tax = line._map_tax_fiscal_position(tax);
-                if(tax.price_include && tax.id != line_tax.id){
+                if(line_tax && tax.price_include && tax.id != line_tax.id){
 
                     mapped_included_taxes.push(tax);
                 }