timestamp 0 is not valid for DateTime('timestamp')

[flydzen]

0 is a valid timestamp, however, an error occurs during parsing

code example:

from marshmallow import fields, Schema


class A(Schema):
    x = fields.DateTime('timestamp')


a = A().load({"x": 0})
print(a)

expected:

{'x': datetime.datetime(1970, 1, 1, 0, 0)}

actual

marshmallow.exceptions.ValidationError: {'x': ['Not a valid datetime.']}

bug line

[deckar01]

It looks like we can safely remove the falsy check in DateTime._deserialize(). Other than a unit test being added to explicitly reject zero timestamps all of the other formats covered by the unit tests continue to reject invalid values with an identical error.

dev...deckar01:marshmallow:2133-zero-timestamp