Strategy for dictionary with optional keys

Currently I am using hypothesis fixed_dictionaries strategy to generate a dictionary with specific keys and data types that are considered valid for my application. I need a strategy which produces this fixed dictionary as well as others with specific keys removed. Or a dictionary with a certain minimal set of keys with optional additional ones, preferably in a way that produces the various combinations of these optional keys.

This is an example of the json schema that needs to be validated, with the 2 optional fields. I'd like to generate all possible valid data for this schema.

'user_stub': {
    '_id':        {'type': 'string'},
    'username':   {'type': 'string'},
    'social':     {'type': 'string'},
    'api_name':   {'type':     'string',
                   'required': False},
    'profile_id': {'type':     'integer',
                   'required': False},
}

This is what I came up with but it is incorrect because it retains the keys but uses None as the value, and I want instead that the keys are removed.

return st.fixed_dictionaries({
    '_id':        st.text(),
    'username':   st.text(),
    'social':     st.text(),
    'api_name':   st.one_of(st.none(),
                            st.text()),
    'profile_id': st.one_of(st.none(),
                            st.integers()),
})