Hello,
I added a field into product.template model called "pieces_inside_1_cartoon" and I want this field to appear into the tree of stock.view_picking_form, so when the user chooses a product, the pieces_inside_1_cartoon appears. 
I keep getting errors concerning that matter.
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Here is the product.template model I inderited:
from odoo import models, fields, api
class StockPicking(models.Model):
    _inherit = 'stock.picking'
    product_id = fields.Many2one("product.template")
    pcs_per_cartoon = fields.Integer(related="product_id.pcs_per_cartoon", string="Number of cartons")
    # pcs_per_cartoon = fields.Integer(string="Number of cartons")
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Here is the view I inherited:
    
        view.picking.form.inherited
        stock.picking
        
        1001
        
            
                
            
                               position="after">
                
            
        
    
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Here is the error I keep getting:
Field "pcs_per_cartoon" does not exist in model "stock.move"
