In 3536f41f00 we added a fallback when setting a
property to a falsy value so that the property was set to the empty string. The
objective being to not get the string "undefined"/"null"/"false" as property
value. However, using t-att- to set a property to 0 is perfectly reasonable and
in fact quite common.
This commit fixes some issues with falsy attributes not being properly
set/removed in various situations. Also, the behaviour was not
consistent between normal attribute (key/value) and generic attributes
(pair or object)
Géry Debongnie