Merge pull request #21 from redcanari/adding-support-for-abstract-tra…

…nsforms

Ignoring transform classes that have a `None` input type.

src/canari/pkgutils/transform.py

@@ -194,7 +194,7 @@ def import_package(pkg):
 
     def find_all_subclasses(self, cls):
         for subclass in cls.__subclasses__():
-            if subclass.__module__.startswith(self._package_name):
+            if subclass.__module__.startswith(self._package_name) and subclass.input_type:
                 yield subclass
             for sub_subclass in self.find_all_subclasses(subclass):
                 yield sub_subclass