trim(null)
is deprecated and was removed from other parts of MediaWiki, cf. T311578.
I see the following output on https://portal.mardi4nfdi.de/wiki/Help:MathTestNative with the current master branch
Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/BaseMethods.php on line 198 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/Util/MMLutil.php on line 160 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/Util/MMLutil.php on line 160 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/BaseMethods.php on line 198 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/Util/MMLutil.php on line 160 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/BaseMethods.php on line 198 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/Util/MMLutil.php on line 160 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/Util/MMLutil.php on line 160 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/BaseMethods.php on line 198 Deprecated: trim(): Passing null to parameter #1 ($string) of type string is deprecated in /var/www/html/extensions/Math/src/TexVC/MMLmappings/Util/MMLutil.php on line 160