Merge pull request #530 from adamralph/patch-2

fix env var condition in Push.ps1

Author: jbogard

Push.ps1

@@ -1,7 +1,7 @@
 $scriptName = $MyInvocation.MyCommand.Name
 $artifacts = "./artifacts"
 
-if ($Env:MYGET_MEDIATR_CI_API_KEY -eq $null) {
+if ([string]::IsNullOrEmpty($Env:MYGET_MEDIATR_CI_API_KEY)) {
     Write-Host "${scriptName}: MYGET_MEDIATR_CI_API_KEY is empty or not set. Skipped pushing package(s)."
 } else {
     Get-ChildItem $artifacts -Filter "*.nupkg" | ForEach-Object {