Xcode 10 Command PhaseScriptExecution failed with a nonzero exit code (EXPANDED_CODE_SIGN_IDENTITY: unbound variable)

This helped me

sudo gem install cocoapods --pre
pod update

I’ve read BugReport. Problem was similar to mine and it was fixed in 1.6.0.beta.1 (2018-08-16) (changelog).

Updated(thanks to Cœur)

1.6.0 (2019-02-07) Was published

sudo gem update cocoapods

This should work now.