code: function mergeDomainRegistrantContactDetails( domainState, registrantContactDetails ) {
  	return isArray( domainState.data )
  		? domainState.data.map( item => {
  				if ( item.type === whoisType.REGISTRANT ) {
  					return {
  						...item,
  						...registrantContactDetails,
  					};
  				}
  				return item;
  		  } )
  		: [
  				{
  					...registrantContactDetails,
  					type: whoisType.REGISTRANT,
  				},
  		  ];
  }
docs: @desc Updates registrant contact details in state[ {domainName} ].data
  
  @param {Object} [domainState] Current state for {domainName}.
  @param {Object} [registrantContactDetails] New registrant contact details
  @return {Array} New data state.