set `role` field to not null

error occurred while creating table appframework_app_enabled
Caused by: liquibase.exception.MigrationFailedException: Migration failed for change set liquibase.xml::appframework-1::djazayeri:
     Reason: liquibase.exception.DatabaseException: Error executing SQL ALTER TABLE `appframework_app_enabled` ADD CONSTRAINT `app_enabled_for_role` FOREIGN KEY (`role`
) REFERENCES `role` (`role`): Can't create table `openmrs`.`#sql-33a_2c4` (errno: 150 "Foreign key constraint is incorrectly formed")

environment: 
Server OS: FreeBSD 10.1-RELEASE (amd64)
JDK version: OpenJDK 7 (1.7.0_71-b14)
Tomcat version: 7.0.57