code: public function process(File $phpcsFile, $stackPtr)
      {
          $tokens = $phpcsFile->getTokens();
  
          if (isset($tokens[$stackPtr]['nested_parenthesis']) === false) {
              // this isn't a default value
              // for a function
              $error = 'Use of null is forbidden';
              $phpcsFile->addError($error, $stackPtr, 'NullUsed');
              $phpcsFile->recordMetric($stackPtr, 'No null members', 'no');
  
              return;
          }
  
          // Check to see if this including statement is within the parenthesis
          // of a function.
          foreach ($tokens[$stackPtr]['nested_parenthesis'] as $left => $right) {
              $allowedPlacement = ['T_FUNCTION', 'T_IF', 'T_ELSEIF'];
              if (! isset($tokens[$left]['parenthesis_owner']) === true ||
                  ! in_array($tokens[$tokens[$left]['parenthesis_owner']]['type'], $allowedPlacement)) {
                  // this isn't a default value
                  // for a function
                  $error = 'Use of null is forbidden';
                  $phpcsFile->addError($error, $stackPtr, 'NullUsed');
                  $phpcsFile->recordMetric($stackPtr, 'No null members', 'no');
  
                  return;
              }
          }
      }
docs: {@inheritdoc}