Add regression test case for MANG-561
Add regress test case for MAGN-616
Add regress test case for MAGN-618
Add regress test case for MAGN-586
Fix MAGN-600: CBN remembers the last computed value of a variable
Add null check for returned errors in CBN
Fix preview for CBN not update when there is an error in CBN
Merge pull request #737 from ke-yu/ChocoButter

Add test cases and defect fixing