Whistling Past the Graveyard

informal

: to act or talk as if one is relaxed and not afraid when one is actually afraid or nervous He shows a confident manner, but he may just be whistling past the graveyard.

(idiomatic, US) To attempt to stay cheerful in a dire situation; to proceed with a task, ignoring an upcoming hazard, hoping for a good outcome. 

 

I found that in the Middle Ages and even into the 1800s, cemeteries were often built on the edges of a town. ... To escape these ghostly encounters, travelers would make loud noises or literally whistle as they walked past the graveyard to keep the spirits and their own fear away until they were past the cemetery.Oct 31, 2011 https://ahistoricalslant.blogspot.com/2011/10/whistling-past-graveyard.html