Fix a bug where thread owners Avatar was used if post owner

did not have one.  This is due to behavior in HTML::Template
with global_vars=1.  If a loop variable is undef, then the global
will be used instead.  Using empty string '' is a better solution.
'' and undef are both false, so template conditionals will not
be changed.

docs/changelog/7.x.x.txt

@@ -7,6 +7,7 @@
    test collateral directory.  The method is called getTestCollateralPath.
    Existing tests using that directory have been modified to use the new
    method instead of finding the path manually.
+ - fix: Avatar in Thread & Posts of CS
 
 7.3.1
  - Fixed a problem with IE and resizable text areas that caused IE to crash

lib/WebGUI/Asset/Post.pm

@@ -317,14 +317,14 @@ Returns a URL to the owner's avatar.
 
 sub getAvatarUrl {
 	my $self = shift;
-	my $avatarUrl;
 	my $parent = $self->getThread->getParent;
-	return undef unless $parent;
-	return $avatarUrl unless $parent->getValue("avatarsEnabled");
+	return '' unless $parent and $parent->getValue("avatarsEnabled");
 	my $user = WebGUI::User->new($self->session, $self->get('ownerUserId'));
 	#Get avatar field, storage Id.
 	my $storageId = $user->profileField("avatar");
+	return '' unless $storageId;
 	my $avatar = WebGUI::Storage::Image->get($self->session,$storageId);
+	my $avatarUrl = '';
 	if ($avatar) {
 		#Get url from storage object.
 		foreach my $imageName (@{$avatar->getFiles}) {