[web2py] error: ('IS_IN_SET' object has no attribute 'startswith')

[Chandrakant Kumar]

I'm passing a tuple of strings to IS_IN_SET validator, but i'm getting  
this error -

<type 'exceptions.AttributeError'>('IS_IN_SET' object has no attribute  
'startswith')

code is - Field('state', IS_IN_SET(STATE_LIST)),

where STATE_LIST is a tuple of strings.
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