No, that is not possible. If there is a key present there is also a value. The value could be undefined though.

exists  $hash {key} && print "Key is present, value may be undefined."
+;
defined $hash {key} && print "Key is present, and its value is defined
+.";
        $hash {key} && print "Key is present, its value is defined and
+ true.";
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Of course, this is also documented in the manual: perldoc -f exists.

Abigail