PowerShell: Struggling with If Statements

i have problems of understanding values of variables in PowerShell and I check them with if statements.

$LDAPDirectoryService = '10.10.XXX.XXX:389'
$DomainDN = 'o=Enterprise'
#$LDAPFilter = '(&(objectCategory=Person)(memberOf=cn=alc-01-Planung-rw,ou=KT,o=enterprise))'

$LDAPFilter = '(&(cn=alc-01-Planung-rw))'
#$LDAPFilter = '(&(cn=XXX))'

$null = [System.Reflection.Assembly]::LoadWithPartialName('System.Net')

$LDAPServer = New-Object System.DirectoryServices.Protocols.LdapConnection $LDAPDirectoryService
$LDAPServer.AuthType = [System.DirectoryServices.Protocols.AuthType]::Anonymous

$Scope = [System.DirectoryServices.Protocols.SearchScope]::Subtree
$AttributeList = @('*')

$SearchRequest = New-Object System.DirectoryServices.Protocols.SearchRequest -ArgumentList $DomainDN,$LDAPFilter,$Scope,$AttributeList


$groups = $LDAPServer.SendRequest($SearchRequest)
$groups

**if($groups -eq $null) {"No Group found"}
if($groups -eq " ") {"No Group found"}**

foreach ($group in $groups.Entries) 
{
  $users=$group.attributes['member'].GetValues('string') 
foreach ($user in $users) {

    Write-Host $user
  }
}

I want to check if the Group exists and then if Users are existing in this group. I tried many statements but none of them seems to work. Its not null or blank, even when nothing is written down in the console.

This is what I got when I use group which doesnt exist

Can anybody show me a solution? Thanks a lot