[web2py] AttributeError: 'Expression' object has no attribute 'strip'

[ukolo]

Receiving the following error in my DB Setup and can't figure it out

Traceback (most recent call last):
  File "gluon/restricted.py", line 186, in restricted
    exec ccode in environment
  File "/home/www-data/web2py/applications/Working/models/db.py", line
60, in <module>
    SQLField('price','double',db.add_product.price))
  File "gluon/sql.py", line 1359, in define_table
    t._create(migrate=migrate, fake_migrate=fake_migrate)
  File "gluon/sql.py", line 1716, in _create
    referenced = field.type[10:].strip()
AttributeError: 'Expression' object has no attribute 'strip'

this is the table

db.define_table('product',
    SQLField('name',db.add_product.name),
    SQLField('category',db.category, requires=IS_IN_DB(db.category.id,
db.category.name)),
    SQLField('description',db.add_product.description),
    SQLField('small_image','upload'),
    SQLField('large_image','upload',db.add_product.image),
    SQLField('quantity','integer',db.add_product.quantity),
    SQLField('price','double',db.add_product.price))

Any help would be appreciated