[web2py] json - Not Serializable error

[lyn2py]

When I perform:

rows = db(db.table.id>0).select()
return rows

It is OK

But when I perform:
rows = db(db.table.id>0).select()
dummy = []
for r in rows:
    if some_condition:
        r.item=False
        dummy.append(r)
    else:
        dummy.append(r)
return dummy

I get the not serializable error. What am I doing wrong?

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