I faced a "bug" today that made me spent 1h figuring out what was going on:

I'm using an external component that accepts a `color` prop in order to set the `background-color` of the root element, but this same component also accepts a `background` prop which I wasn't passing, and by default, it was set to `''`.

The result: React didn't throw an error nor a warning, however, the resulting element in the DOM didn't contain either `background-color` or `background`, and since the element had a default `background-color` coming from a CSS class, it took me a while to figure out why the color that I was passing wasn't being applied, and instead it was using the one from the CSS class.

See: https://codesandbox.io/s/react-example-8rxc8

What I reported above was the `static1` case.

I added other cases as a bonus, as when I was playing with this they also seemed weird to me. On `static2` I define the same properties, but because I change the order, it works. On the toggleable ones, initially I can see the background, but after changing it never appears anymore.

I'm not sure if I created those extra "test cases" correctly. My main concern is really around static1 not outputting anything on the console as a warning.

Related issues:
#6348
#8689

I wonder if #14181 (@sophiebits) should have covered this?
export const enableSchedulerTracing = __PROFILE__;
export const enableSchedulerDebugging = true;
export const replayFailedUnitOfWorkWithInvokeGuardedCallback = false;
export const warnAboutDeprecatedLifecycles = true;
export const warnAboutShorthandPropertyCollision = false;
export const disableLegacyContext = false;
export const warnAboutStringRefs = false;
export const warnAboutDefaultPropsOnFunctionComponents = false;
export const disableSchedulerTimeoutBasedOnReactExpirationTime = false;
export const enableTrainModelFix = true;
export const exposeConcurrentModeAPIs = __EXPERIMENTAL__;
export const enableSuspenseServerRenderer = true;
export const enableSelectiveHydration = true;
export const enableChunksAPI = __EXPERIMENTAL__;
export const disableJavaScriptURLs = true;
let refCount = 0;
export function addUserTimingListener() {
  if (__DEV__) {
    
    return () => {};
  }
  refCount++;
  updateFlagOutsideOfReactCallStack();
  return () => {
    refCount--;
    updateFlagOutsideOfReactCallStack();
  };
}
let timeout = null;
function updateFlagOutsideOfReactCallStack() {