I have inheritted survey_user_input and added 

lead_id = fields.Many2one(comodel_name='crm.lead', string='Crm Lead') 

and i wanted to show this in the smart  button 

<button name="action_open_documents"
            class="oe_right_oe_button_box"
            icon="fa-star"
            string="Lead"
            type="object"
            invisible="not lead_id" >

</button>

the method is :

def action_open_lead(self):
    return {
        'type': 'ir.actions.act_window',
        'name': 'Lead',
        'res_model': 'crm.lead',
        'view_mode': 'form',
        'res_id': self.lead_id.id,
        'context': {'create': False}
    }

the xpath is correct because the other  buttons which i have  creaqted in  this model  works but for this i get :

Field 'lead_id' used in modifier 'invisible' (not lead_id) is restricted to the group(s) base.group_no_one.

View error context:

{'file': '/home/guhan/odoo/opt/odoo-servicum-addons/servicum_fillout_integration/views/survey_user_input_inherit.xml',

'line': 1,

'name': 'survey.user.input.view.form.inherit',

'view': ir.ui.view(772,),

'view.model': 'survey.user_input',

'view.parent': ir.ui.view(560,),

'xmlid': 'survey_user_input_view_form_inherit'}

i  get  the error only when 

invisible="not lead_id" 

is present.i have no groups set up in the field definition. the lead_id many2one alone works , but  it throws an error in  the button . any help would  be appreciated. Thanks