This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
_current,
  workInProgress,
  elementType,
  updateLanes,
  renderLanes,
) {
  if (_current !== null) {
    
    
    
    
    _current.alternate = null;
    workInProgress.alternate = null;
    
    workInProgress.flags |= Placement;
  }
  const props = workInProgress.pendingProps;
  const lazyComponent: LazyComponentType<any, any> = elementType;
  const payload = lazyComponent._payload;
  const init = lazyComponent._init;
  let Component = init(payload);
  
  workInProgress.type = Component;
  const resolvedTag = (workInProgress.tag = resolveLazyComponentTag(Component));
  const resolvedProps = resolveDefaultProps(Component, props);
  let child;
  switch (resolvedTag) {
    case FunctionComponent: {
      if (__DEV__) {
        validateFunctionComponentInDev(workInProgress, Component);