If you pass "nocopyright" then MediaWiki's copyright icon will not be included
in the list of footer icons. This is mostly useful for skins which only
display the text from footericons instead of the images and don't want a
duplicate copyright statement because footerlinks already rendered one.
But even after using BaseTemplate::getFooterIcons( 'nocopyright' ), the copyright icon will still be included.
and BaseTemplate::getFooterIcons( 'nocopyright' ) === BaseTemplate::getFooterIcons() is true. This will lead to duplicate rights text that is ought to be avoided, and may raise undefined 'alt' index PHP notice if $wgRightsIcon and $wgRightsText are falsey. They're by default and will be set to empty string if "no license footer" is set during installation.
... } elseif ( $option == 'nocopyright' ) { unset( $footericons['copyright']['copyright'] ); if ( $footericons['copyright'] === [] ) { unset( $footericons['copyright'] ); } }