code: public static void onOperatorError(BiFunction<? super Throwable, Object, ? extends Throwable> onOperatorError) {
  		onOperatorError(onOperatorError.toString(), onOperatorError);
  	}
docs: Add a custom error mapping, overriding the default one. Custom mapping can be an
  accumulation of several sub-hooks each subsequently added via this method.
  <p>
  Note that sub-hooks are cumulative, but invoking this method twice with the same
  instance (or any instance that has the same `toString`) will result in only a single
  instance being applied. See {@link #onOperatorError(String, BiFunction)} for a variant
  that allows you to name the sub-hooks (and thus replace them or remove them individually
  later on). Can be fully reset via {@link #resetOnOperatorError()}.
  <p>
  For reference, the default mapping is to unwrap the exception and, if the second
  parameter is another exception, to add it to the first as suppressed.
  
  @param onOperatorError an operator error {@link BiFunction} mapper, returning an arbitrary exception
  given the failure and optionally some original context (data or error).
  
  @see #onOperatorError(String, BiFunction)
  @see #resetOnOperatorError(String)
  @see #resetOnOperatorError()