Beware of default values. Set them yourself.
IBM, in its infinite wisdom, defaulted all numeric variables to zero, except for one type. It took me 6 weeks to discover that (when using cards and two tests per day for a program). With current technology, that would have converted to days.
A few years later, they switched that data type with another one figuring that it didn’t make any difference. The company had to run an emulation environment of the old operating system to run that app. It increased the company’s market share by 20% when implemented, so that couldn’t just shut it down.
It ran for 18 years without a single upgrade, before it was replaced with an off-the-shelf product.