some1 has deleted my issue for the same, I do not know why? Thanks for raising it
I can run normally in the Swift 5.0 project.
https://github.com/tristanhimmelman/ObjectMapper/issues/1043
Parsing complicated object with optional objects as a parameter works with workaround only
WORKAROUND
pod 'ObjectMapper', git: 'https://github.com/cddjr/ObjectMapper.git', branch: 'swift-5'