About 6 months into my first proper gig I was working on some code for emailing people in estate agencies. Typically you've got three channels, Rental, Sales and Commercial there. This was a Java Spring app and I didn't really understand all the annotation magic, and the channel field was nullable as to make it non-null you needed to write a @NotNull annotation above it. To add insult to injury I gave the field the wrong name too, it was agentChannel, not channel.

I then wrote some code like:

  if (channel == AgentChannel.sales) {
     emailSales()
  } else {
     emailRentalOrCommercial()
  }

So when parsing the JSON, the field name silently failed and all emails got sent to rental or commercial channels.

Sales is obviously the most lucrative channel with the biggest contingent of, shall I say, "pushy" people and so when this was discovered I had quite an upsetting day.