result.data is empty, thats why it has error, to fix this you have to add check in:
/nodebb-plugin-ns-custom-fields/app/filters.js from line 24:

            if (result.data) { 
            var i = 0, len = result.fields.length, fieldMeta, customFields = [];
            for (i; i < len; ++i) {
                fieldMeta = result.fields[i];
                var value = result.data[fieldMeta.key];
                if (value) {
                    customFields.push({
                        name : fieldMeta.name,
                        value: value
                    });
                }
            }
            params.userData.customFields = customFields;
            }            
            callback(null, params);

@Nicolas can you show template changes for account/edit.tpl file. I found it in nodebb-plugin-ns-custom-fields/templates/account/edit.tpl