Navigation.php is used on every page, so any error being thrown by it will hit the system.log. Since the functions in this file may be called multiple times per page view it can cause an exponential number of entries to be pushed into the system.log file.
Your problem is not in this file. Your problem comes from another process calling functions within the Navigation.php block. Something’s likely messed up in a template somewhere and it’s failing to pass the $rendermode variable in the function call. As Navigation.php doesn’t have an error handler for this missing item, you will have to search for the following function calls and find where the variable is missing from the call.
Function calls that expect $rendermode to be passed to them are:
protected function _renderCategoryMenuItemHtml($category, $level = 0, $isLast = false, $isFirst = false,
$isOutermost = false, $outermostItemClass = ‘’, $childrenWrapClass = ‘’, $noEventAttributes = false, $rendermode)
public function drawItem($category, $level = 0, $last = false, $rendermode)
Find where these are being used elswhere and why they’re not passing $rendermode