Dear helpers,

I am stuck in the error showing in the title. Below are my codes. The error occurs at this command below as it did not pop up the error when I commented this line. 

I have no clue what I should do to fix this error.  These codes are to turn on "Quality Check" button if "picking_obj" is in "assigned" state.

​rec.show_quality_check_btn = True

python file

class Picking(models.Model):
    _inherit = "stock.picking"  
	​
	​show_quality_check_btn = fields.Boolean(default=False, compute='_compute_show_quality_check_btn') 

@api.depends('state')
def _compute_show_quality_check_btn(self): 
	​for rec in self:
    	​picking_obj = rec.filtered(lambda p: p.state == 'assigned')  # assigned = Ready
    	​if picking_obj:
         	​rec.show_quality_check_btn = True

Error details 

OwlError: An error occured in the owl lifecycle (see this Error's "cause" property)
    at handleError (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:916:101)
    at App.handleError (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:1542:29)
    at Fiber._render (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:941:19)
    at Fiber.render (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:939:6)
    at ComponentNode.initiateRender (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:1007:47)

Caused by: TypeError: Cannot read properties of undefined (reading 'map')
    at get tags (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:7901:67)
    at Many2ManyTagsFieldColorEditable.template (eval at compile (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:1500:374), :15:26)
    at Fiber._render (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:940:96)
    at Fiber.render (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:939:6)
    at ComponentNode.initiateRender (http://localhost:8069/web/assets/2cca91a/web.assets_web.min.js:1007:47)