perldoc -f exists

    undef $ref;
    if (exists $ref->{"Some key"})      { }
    print $ref;             # prints HASH(0x80d3d5c)

##</code><code>##

  This surprising autovivification in what does not at first--or
  even second--glance appear to be an lvalue context may be fixed
  in a future release.

##</code><code>##

C:\>perl -e "undef $ref; if (exists $ref->{'key1'}->{'key2'})
{print 'I think i am okay, but...'}; print keys %{$ref}"
key1