val.diff

diff --git a/lib/Mojo/DOM.pm b/lib/Mojo/DOM.pm
index 62c66b7..f03fe9f 100644
--- a/lib/Mojo/DOM.pm
+++ b/lib/Mojo/DOM.pm
@@ -165,12 +165,12 @@ sub val {
   # "option"
   return $self->{value} // $self->text if (my $tag = $self->tag) eq 'option';
 
-  # "select"
-  return $self->find('option:checked')->map('val')->to_array
-    if $tag eq 'select';
-
   # "textarea", "input" or "button"
-  return $tag eq 'textarea' ? $self->text : $self->{value};
+  return $tag eq 'textarea' ? $self->text : $self->{value} if $tag ne 'select';
+
+  # "select"
+  my $v = $self->find('option:checked')->map('val');
+  return exists $self->{multiple} ? $v->size ? $v->to_array : undef : $v->first;
 }
 
 sub wrap         { shift->_wrap(0, @_) }
@@ -945,10 +945,10 @@ C<root>, C<tag> or C<text>.
 
   my $value = $dom->val;
 
-Extract values from C<button>, C<input>, C<option>, C<select> and C<textarea>
-elements or return C<undef> if this element has no value. In the case of
-C<select>, find C<option> elements with C<selected> attribute and return an
-array reference with all values.
+Extract value from C<button>, C<input>, C<option>, C<select> and C<textarea>
+element or return C<undef> if this element has no value. In the case of
+C<select> with C<multiple> attribute, find C<option> elements with C<selected>
+attribute and return an array reference with all values.
 
   # "a"
   $dom->parse('<input name="test" value="a">')->at('input')->val;
@@ -964,6 +964,10 @@ array reference with all values.
 
   # "e"
   $dom->parse('<select><option selected>e</option></select>')
+    ->at('select')->val;
+
+  # "f"
+  $dom->parse('<select multiple><option selected>f</option></select>')
     ->at('select')->val->[0];
 
 =head2 wrap
diff --git a/lib/Mojo/Parameters.pm b/lib/Mojo/Parameters.pm
index 1ead7aa..bbfabaa 100644
--- a/lib/Mojo/Parameters.pm
+++ b/lib/Mojo/Parameters.pm
@@ -21,7 +21,7 @@ sub append {
     if (ref $value eq 'ARRAY') { push @$old, $name => $_ // '' for @$value }
 
     # Single value
-    else { push @$old, $name => $value }
+    elsif (defined $value) { push @$old, $name => $value }
   }
 
   return $self;
diff --git a/lib/Mojo/UserAgent/Transactor.pm b/lib/Mojo/UserAgent/Transactor.pm
index 028b96d..9920424 100644
--- a/lib/Mojo/UserAgent/Transactor.pm
+++ b/lib/Mojo/UserAgent/Transactor.pm
@@ -192,7 +192,7 @@ sub _multipart {
 
   my @parts;
   for my $name (sort keys %$form) {
-    my $values = $form->{$name};
+    next unless defined(my $values = $form->{$name});
     for my $value (ref $values eq 'ARRAY' ? @$values : ($values)) {
       push @parts, my $part = Mojo::Content::Single->new;
 
diff --git a/t/mojo/dom.t b/t/mojo/dom.t
index 391dbcc..4cd713a 100644
--- a/t/mojo/dom.t
+++ b/t/mojo/dom.t
@@ -2189,6 +2189,7 @@ $dom = Mojo::DOM->new(<<EOF);
     <option value="J" selected>K</option>
   </select>
   <select name="n"><option>N</option></select>
+  <select multiple name="q"><option>Q</option></select>
   <select name="d"><option selected>D</option></select>
   <textarea name="m">M</textarea>
   <button name="o" value="O">No!</button>
@@ -2203,8 +2204,10 @@ is_deeply $dom->at('select')->val, ['I', 'J'], 'right values';
 is $dom->at('select option')->val,                          'F', 'right value';
 is $dom->at('select optgroup option:not([selected])')->val, 'H', 'right value';
 is $dom->find('select')->[1]->at('option')->val, 'N', 'right value';
-is_deeply $dom->find('select')->[1]->val, [], 'no values';
-is_deeply $dom->find('select')->last->val, ['D'], 'right values';
+is $dom->find('select')->[1]->val,        undef, 'no value';
+is_deeply $dom->find('select')->[2]->val, undef, 'no value';
+is $dom->find('select')->[2]->at('option')->val, 'Q', 'right value';
+is_deeply $dom->find('select')->last->val, 'D', 'right value';
 is $dom->at('textarea')->val, 'M', 'right value';
 is $dom->at('button')->val,   'O', 'right value';
 is $dom->find('form input')->last->val, 'P', 'right value';