unable to get the last build number fro the jobs

[RASHMI BS]

last_build_number = server.get_job_info('api-test')['lastCompletedBuild']['number']

i have tried to use the above code to get the last completed job for the currently stable build in jenkins

i don't see the desired result

i could see the below error
TypeError: 'NoneType' object has no attribute '__getitem__'

and when i have tried this

last_build_number = server.get_job_info('api-test')['lastCompletedBuild']

it returned 1

where in the job contains 100+ builds

please share the code snippet to get the latest successfull build number from jenkins