running pipeline from PR policy

[czechdude]

When I try to run the pipeline from a Pull request as policy, it does not detect files and throws fatal: bad object to every commit.

##[debug]Build.BuildId=65047
##[debug]Build.SourceBranch=refs/pull/7325/merge
##[debug]CF:::Build ID: 65047
##[debug]CF:::Reference Branch: undefined
##[debug]CF:::Current Branch: refs/pull/7325/merge
##[debug]CF:::> Extracting changes from the list of commits...
##[debug]CF:::> Getting the list of changes for the build 65047
##[debug]CF:::> Executing: git log -m -1 --name-only --pretty=format: 1c43dd786ce56183c262a6fe3be83d6e297ab049
##[debug]which 'git'
##[debug]found: '/usr/bin/git'
##[debug]/usr/bin/git arg: ["log","-m","-1","--name-only","--pretty=format:","1c43dd786ce56183c262a6fe3be83d6e297ab049"]
##[debug]/usr/bin/git arg: ["log","-m","-1","--name-only","--pretty=format:","1c43dd786ce56183c262a6fe3be83d6e297ab049"]
##[debug]exec tool: /usr/bin/git
##[debug]exec tool: /usr/bin/git
##[debug]arguments:
##[debug]arguments:
##[debug]   log
##[debug]   log
##[debug]   -m
##[debug]   -m
##[debug]   -1
##[debug]   -1
##[debug]   --name-only
##[debug]   --name-only
##[debug]   --pretty=format:
##[debug]   --pretty=format:
##[debug]   1c43dd786ce56183c262a6fe3be83d6e297ab049
##[debug]   1c43dd786ce56183c262a6fe3be83d6e297ab049
/usr/bin/git log -m -1 --name-only --pretty=format: 1c43dd786ce56183c262a6fe3be83d6e297ab049
fatal: bad object 1c43dd786ce56183c262a6fe3be83d6e297ab049