Input parameter null checking for AstFactory methods
Merge pull request #3240 from Randy-Ma/master

Add missing files and adjust the path for two test cases
Never return null for AstIdentifierBase unless has error
Merge pull request #3243 from ke-yu/fix_magn5096

Fix magn5096: AstFactory methods require null checks
Merge branch 'master' into Revit2015
Merge pull request #3245 from ke-yu/Revit2015

Merge master into Revit2015