[PHP 8.1 compatibility] Deprecated - preg_split(): Passing null to parameter #2 ($subject) of type string is deprecated in Draw.php(2302)

[tsteur]

vendor/szymach/c-pchart/src/Draw.php(2302): Deprecated - preg_split(): Passing null to parameter #2 ($subject) of type string is deprecated - Matomo 4.14.3-b1 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already) [internal function]: Piwik\ErrorHandler::errorHandler(),#1/vendor/szymach/c-pchart/src/Draw.php(2302),#2/plugins/ImageGraph/StaticGraph/GridGraph.php(312),#3/plugins/ImageGraph/StaticGraph/Evolution.php(24),#4/plugins/ImageGraph/API.php(506),[internal function]: Piwik\Plugins\ImageGraph\API->get(),#6/core/API/Proxy.php(244),#7/core/Context.php(28),#8/core/API/Proxy.php(335),#9/core/API/Request.php(267)

After upgrading to PHP 8.1 above warning is showing up in the logs. This is all the information we have.

[michalkleiner]

Hi @tsteur,
thanks for reporting this. I've checked and we are using the latest version of szymach/c-pchart that draws the graphs and this issue may occur when the data series to display doesn't have a description which is attempted to be split into lines of text.

This issue is the same problem as #20656 so I will mark that one as a duplicate and we'll address all occurrences of the same code (preg_split("/\n/", $Serie["Description"]);) together. We will need to make sure we always pass at least an empty string, not a null as the data series description.

[sgiehl]

@michalkleiner As the description should actually not be a required property of a data series, this might also be a a bug in szymach/c-pchart. We can also try to create a PR there and try to get that merged. I've already provided a couple of fixes for that lib...

[michalkleiner]

Yes, that's a good point. We can approach it from either direction — either make sure we always pass at least an empty string (not a null value) or submit a PR for the c-pchart dependency to correctly handle optional descriptions with null coalesce operator.

[sgiehl]

Had another look through the code and it seems it's actually a problem on our side and not the library. The library automatically sets the Description if new datapoints are added. But I found a place where it can happen that the description is overwritten with null on our side. Will propose a PR to fix that.