No need for the "()" around a single my variable declaration
This is true in most situations but not all. From the OP's code: 
  my ( $Ref_to_Hash ) = @_;

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In this style of parameter initialization, the parentheses are in fact required. Otherwise $Ref_to_Hash will be assigned the number of arguments, not the value of the first one.

In reply to Re^2: Modify a hash via its reference by Errto
in thread Modify a hash via its reference by Philippe

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