getElementByid("myObhectId") return null???

[qtptester]

Hello
I tried to look for the answer to my question before open a new topic but i did not founded it
i try to get and object of type webbutton from my application :

Code:

set input=Browser("title:=.*").page("title:=.*").Object.getElementByid("myObhectId")

then i clcik on it :

input.click

i have problems when the object is not present in the page
how can i test if getElementByid("myObhectId") returns an objecT?
i tried with following methos
isnull(input)
isobject(input)
but thet seem not work

thank in advance for your help
Dave