code: func (b *MultiErrorBuilder) ErrOrNil() error {
  	// No errors added, return nil.
  	if len(b.errors) == 0 {
  		return nil
  	}
  
  	// Return a single error when there is only one and the builder is told to do so.
  	if len(b.errors) == 1 && b.SingleWrapMode == ReturnSingle {
  		return b.errors[0]
  	}
  
  	return &multiError{b.errors, b.Message}
  }
docs: // ErrOrNil returns a MultiError the builder aggregates a list of errors,
  // or returns nil if the list of errors is empty.
  //
  // It is useful to avoid checking if there are any errors added to the list.