Earlier quoted context omitted.
I don't know about their code quality, but we consume some of their data via APIs and they periodically randomly change their non-nullable data types to nullable. Fun times hotfixing those in prod.
When data comes in over the wire, you probably shouldn't be making assumptions about what's nullable. You should write a parser that fails gracefully if it receives unexpected input. It's the robustness principle. https://en.wikipedia.org/wiki/Robustness_principle
I have to work with their APIs often (as well as Amazon, Facebook and a couple other big players, they're all equally awful).
Their documentation will tell you a type is an integer and will never be null. They will do this for 3 months, and then change it to send a string that can be nullable or empty string, without telling you or updating API versions. It goes beyond robustness. It's the "BigCorp will actively lie to you in their documentation" principle.