Currently, the API is returning is a null value for some rocket.agencies. This causes your notebook to break. You can default the length to 0 with num_agencies: row.rocket.agencies?.length || 0

Great find! Wasn't sure if optional chaining was used widely, but it looks safe. Thanks for fixing this! https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Optional_chaining