Trying to push onto a hashref will produce an error so my guess is that $data_b is coming back from wherever as an AoH to begin with.

  DB<1> $a = { qw/ foo bar/ }

  DB<2> $b = { qw/baz quux/ }

  DB<3> x +{ %$a, %$b }
0  HASH(0x7ff1242138f0)
   'baz' => 'quux'
   'foo' => 'bar'
  DB<4> x push @{ $b }, $a
Not an ARRAY reference at (eval 17)[/System/Library/Perl/5.18/perl5db.
+pl:732] line 2.
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