Still hitting problems. I enter some details, pick what I think is the third theme, choose a shade of orange, then in the accent colour field press backspace, and it dies.

  TypeError: "can't access property "r", r is null"
    ye Gengar.js:7
    React 7
    unstable_runWithPriority scheduler.production.min.js:19
    React 9
    unstable_runWithPriority scheduler.production.min.js:19
    React 18
    251 index.js:20
    i (index):1
    70 main.f5214b72.chunk.js:1
    i (index):1
    t (index):1
    r (index):1
    <anonymous> main.f5214b72.chunk.js:1
  react-dom.production.min.js:209:194
  TypeError: can't access property "r", r is null
  Gengar.js:7:21