Checking JavaScript object for null subtelty

Checking JavaScript object for null subtelty

Unless you are really sure, please don't come and tell me this question
has already been asked and answered.
OK, so I believe I have found cases where I need to check for both
undefined and null for a javascript object as follows:
if (x !== undefined && x != null && x.length > 0) {...}
However, in a recent upgrade of JetBrains tools, it tells me that this is
sufficient
if (x != undefined && x.length > 0) {...}
My question is, I'm just wanting to insure that a string "x" has a length
of non-zero and is not undefined or null (with the least amount tests).
Thoughts?