Avoid warnings in filters callback when undef is pushed to the conten…

…t body array. Fixes plackgh-92

lib/HTTP/Message/PSGI.pm

@@ -113,7 +113,7 @@ sub _res_from_psgi {
         $res->headers->header(@$headers) if @$headers;
 
         if (ref $body eq 'ARRAY') {
-            $res->content(join '', @$body);
+            $res->content(join '', grep defined, @$body);
         } else {
             local $/ = \4096;
             my $content;

lib/Plack/Component.pm

@@ -55,7 +55,8 @@ sub response_cb {
                         $line = $filter_cb->($line);
                     }
                     # Send EOF.
-                    push @{ $res->[2] }, $filter_cb->( undef );
+                    my $eof = $filter_cb->( undef );
+                    push @{ $res->[2] }, $eof if defined $eof;
                 } else {
                     my $body    = $res->[2];
                     my $getline = sub { $body->getline };

t/Plack-Middleware/component.t

@@ -0,0 +1,41 @@
+use strict;
+use Test::Requires qw(IO::Handle::Util);
+
+package MyComponent;
+use parent 'Plack::Component';
+use Plack::Util::Accessor qw( res cb );
+
+sub call { return $_[0]->response_cb( $_[0]->res, $_[0]->cb ); }
+
+package main;
+use IO::Handle::Util qw(:io_from);
+use HTTP::Request::Common;
+use Test::More;
+use Plack::Test;
+
+# Various kinds of PSGI responses.
+my @res = (
+    [200, ['Content-Type' => 'text/plain'], ['Hello']],
+    [200, ['Content-Type' => 'text/plain'], io_from_array ['Hello']],
+    sub { $_[0]->([ 200, ['Content-Type' => 'text/plain'], ['Hello'] ]) },
+    sub {
+        my $writer = $_[0]->([ 200, ['Content-Type' => 'text/plain'] ]);
+        $writer->write( 'Hello' );
+        $writer->close;
+    },
+);
+
+# $body filters can return undef with no warnings.
+for my $res (@res) {
+    my @warns;
+    local $SIG{__WARN__} = sub { push @warns, @_ };
+
+    my $app = MyComponent->new(
+        res => $res, cb => sub { sub { $_[0] } },
+    );
+    test_psgi( $app, sub { $_[0]->(GET '/') } );
+
+    is_deeply \@warns, [];
+}
+
+done_testing;