Trying to fix #6768: allowing false values in PriorityList
Fixes #6768 : boolean values at priority list should be valid
change return on valid() method
added test for boolean values in ZendTest/Db/Sql/UpdateTest
fixes cs
add new list insert for null
#6773 #6768 - splitting out `UpdateTest` for boolean bound parameters into its own test method with `@group` annotations
#6773 #6768 - adding missing @group annotations
#6773 #6768 - removing unused protected property
#6773 #6768 - removing redundant docblocks, cleaning up comparison operations syntax and simplifying code
Merge branch 'hotfix/#6773-allow-false-values-in-priority-list'

Close #6773
Close #6768
Close #6820
Close #6834
Close #6881