How to test for $null array in PowerShell
It's an array, so you're looking for Count to test for contents.
I'd recommend
$foo.count -gt 0The "why" of this is related to how PSH handles comparison of collection objects
You can reorder the operands:
$null -eq $fooNote that -eq in PowerShell is not an equivalence relation.
if($foo -eq $null) { "yes" } else { "no" }help about_comparison_operators displays help and includes this text:
All comparison operators except the containment operators (-contains, -notcontains) and type operators (-is, -isnot) return a Boolean value when the input to the operator (the value on the left side of the operator) is a single value (a scalar). When the input is a collection of values, the containment operators and the type operators return any matching values. If there are no matches in a collection, these operators do not return anything. The containment operators and type operators always return a Boolean value.