Question

Consider the following XML document:

$xml = [xml] "<root><value>one</value><value>two</value></root>"

And then print the values (with some prefix/suffix):

$xml.root.value | %{"*$_*"}
*one*
*two*

So far so good. However, if the element does not exist, a null item is propagated trough the pipeline:

$xml.root.foo | %{"*$_*"}
**

Why is that? Is there any way to avoid this extra check:

$xml.root.foo | ?{$_} | %{"*$_*"}

It’s easy to forget and it seems error prone.

Answer 1

To turn off the silent fail on missing properties use Set-StrictMode -Version Latest e.g.:

PS> $xml = [xml] "<root><value>one</value><value>two</value></root>"
PS> $xml.root.foo | %{"*$_*"}
**
PS> Set-StrictMode -Version Latest
PS> $xml.root.foo | %{"*$_*"}
Property 'foo' cannot be found on this object. Make sure that it exists.
At line:1 char:1
+ $xml.root.foo | %{"*$_*"}
+ ~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [], PropertyNotFoundException
    + FullyQualifiedErrorId : PropertyNotFoundStrict

Note that this will also catch references to non-existing variables. I highly recommend using Set-StrictMode in this manner as it can save you debugging time for larger scripts.