repr of PYSON Eval with a default PYSON expression ends in a traceback
``` Traceback (most recent call last): File "/home/nicoe/projets/tryton/tryton/trytond/trytond/tests/test_pyson.py", line 69, in test_Eval_default self.assertEqual(repr(expr), "(Eval('foo', Eval('bar', 1)) == 1)") ^^^^^^^^^^ File "/home/nicoe/projets/tryton/tryton/trytond/trytond/pyson.py", line 93, in __repr__ repr(params[0]), self._binary_operator, repr(params[1])) ^^^^^^^^^^^^^^^ File "/home/nicoe/projets/tryton/tryton/trytond/trytond/pyson.py", line 86, in __repr__ params = self.__repr_params__ ^^^^^^^^^^^^^^^^^^^^ File "/home/nicoe/projets/tryton/tryton/trytond/trytond/pyson.py", line 152, in __repr_params__ if self._default != '': ^^^^^^^^^^^^^^^^^^^ File "/home/nicoe/projets/tryton/tryton/trytond/trytond/pyson.py", line 62, in __ne__ return Not(Equal(self, other)) ^^^^^^^^^^^^^^^^^^ File "/home/nicoe/projets/tryton/tryton/trytond/trytond/pyson.py", line 314, in __init__ assert types1 == types2, 'statements must have the same type' ^^^^^^^^^^^^^^^^ AssertionError: statements must have the same type ```
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