function mergeBlocks(blocks) {
  let finalBlock;
  for (const block of blocks) {
    if (finalBlock) {
      // $FlowFixMe - finalBlock is definitely defined
      block.nodes.forEach(node => finalBlock.push(node));
    } else {
      finalBlock = block;
    }
  }
  return finalBlock;
}
Puts the content of all given node blocks into the first one, essentially merging them.