static function mergeField($fieldName, $existingValue, $newValue)
 {
     if ($newValue === null) {
         return $existingValue;
     } elseif ($existingValue === null) {
         return $newValue;
     } elseif ($existingValue === $newValue) {
         return $existingValue;
     }
     $appendWithNewlineFields = array('summary', 'notes');
     $appendWithSpaceFields = array('name_suffix', 'name_prefix');
     $dateFields = array('start_date', 'end_date');
     $nameFields = array('name_first', 'name_middle');
     $numberFields = array('employees', 'revenue', 'endowment');
     if (in_array($fieldName, $appendWithNewlineFields)) {
         return $existingValue . "\n\n" . $newValue;
     } elseif (in_array($fieldName, $appendWithSpaceFields)) {
         return $existingValue . ' ' . $newValue;
     } elseif (in_array($fieldName, $dateFields)) {
         $existingDate = new LsDate($existingValue);
         $newDate = new LsDate($newValue);
         if ($existingDate->howSpecific() > $newDate->howSpecific()) {
             return $existingDate->format();
         } elseif ($existingDate->howSpecific() < $newDate->howSpecific()) {
             return $newDate->format();
         } else {
             if ($existingDate->howSpecific() == LsDate::YEAR_SPECIFIC) {
                 return LsDate::lessOrEqual($existingDate, $newDate) ? $existingDate : $newDate;
             } else {
                 return $existingDate;
             }
         }
     } elseif (in_array($fieldName, $nameFields)) {
         return strlen($existingValue) >= strlen($newValue) || strlen($existingValue) !== 1 ? $existingValue : $newValue;
     } elseif (in_array($fieldName, $numberFields)) {
         return $existingValue == 0 ? $newValue : $existingValue;
     } else {
         return $existingValue;
     }
 }