#3346 fix(taps,targets,mappers): Preserve properties with empty JSON schema when flattening them Pull request opened by edgarrmondragon ## Summary by Sourcery Preserve properties with empty JSON schema when flattening by converting them to string to avoid dropping typeless fields Bug Fixes: • Retain typeless (empty schema) properties during schema flattening and assign them a string type Tests: • Add test to ensure typeless properties are preserved and typed as string after flattening meltano/sdk