TOML::Tiny breaks on null array elements

[hadfl]

TOML::Tiny breaks when there are null array elements (edited since the initial bug report was using a top level array):

given this test:

use TOML::Tiny qw(from_toml to_toml);
use Data::Dumper;

my $data = {
    hash => [
        { a => 1, b => 2 },
        undef,
        { a => 3, b => 4 },
    ]
};

print Dumper $data;

my $data_t = to_toml $data;

print $data_t, "\n";

my $data_ = from_toml $data_t;

print Dumper $data_;

it leads to this:

$VAR1 = {
          'hash' => [
                      {
                        'a' => 1,
                        'b' => 2
                      },
                      undef,
                      {
                        'a' => 3,
                        'b' => 4
                      }
                    ]
        };
Use of uninitialized value $data in pattern match (m//) at /build/zadm/thirdparty/lib/perl5/TOML/Tiny/Writer.pm line 73.
Use of uninitialized value $data in pattern match (m//) at /build/zadm/thirdparty/lib/perl5/TOML/Tiny/Writer.pm line 74.
Use of uninitialized value $arg in substitution (s///) at /build/zadm/thirdparty/lib/perl5/TOML/Tiny/Writer.pm line 215.
Use of uninitialized value $arg in substitution (s///) at /build/zadm/thirdparty/lib/perl5/TOML/Tiny/Writer.pm line 216.
Use of uninitialized value $arg in concatenation (.) or string at /build/zadm/thirdparty/lib/perl5/TOML/Tiny/Writer.pm line 218.
hash=[
  {a=1, b=2},
  "",
  {a=3, b=4},
]
$VAR1 = {
          'hash' => [
                      {
                        'a' => 1,
                        'b' => 2
                      },
                      '',
                      {
                        'b' => 4,
                        'a' => 3
                      }
                    ]
        };