human
Solve the following python programming problem given the following code:
def test_optional_to_optional(self) : 
    '
        Test error due mishandling of Optional to Optional casting

        Related issue: https://github.com/numba/numba/issues/1718
        ' 
    opt_int = types.Optional (types.intp) 
    opt_flt = types.Optional (types.float64) 
    sig = opt_flt (sig) 
    @ njit (sig) 
    def foo(a) : 
        return a 
self.assertEqual (foo (2), 2) 
    self.assertIsNone (foo (None)) 

    
    

    Fix the buggy line: sig = opt_flt (sig)
assistant
#Here is Python program to fix the buggy line: sig = opt_flt (sig)
.

sig = opt_flt (opt_int)