Revert "Added isAbstract()"

This reverts commit c9143aaf7ba2dc98224e9c1c4a8f0632cf2dcf93.
Revert "Revert "Added isAbstract()""

This reverts commit eb35117afa634de6e976ab7d4af0b7284a1357d9.
Revert "Revert "Revert "Added isAbstract()"""

This reverts commit 18b53d9fb9a2a7acebb099d2b00d75f48d6961c3.