message: PR Add cstddef include to fix nullptr_t reference
  issues
  GitHub PR
  Copybara import of the project:
  add cstddef inlcude to fix nullptr reference by Alexander Mann
  change nullptr_t to std::nullptr_t by Alexander Mann
  Closes
diff: #ifndef VERIBLE_COMMON_TEXT_TREE_UTILS_H_
  #define VERIBLE_COMMON_TEXT_TREE_UTILS_H_
  +#include <cstddef>
  #include <functional>
  #include <iosfwd>
  @@ -112,7 +113,8 @@ const SyntaxTreeNode* CheckOptionalSymbolAsNode(const SPtr& symbol,
  // Specialization for nullptr_t.
  template <typename E>
  -const SyntaxTreeNode* CheckOptionalSymbolAsNode(const nullptr_t& symbol, E) {
  +const SyntaxTreeNode* CheckOptionalSymbolAsNode(const std::nullptr_t& symbol,
  + E) {
  return nullptr;
  }
  @@ -127,7 +129,8 @@ const SyntaxTreeLeaf* CheckOptionalSymbolAsLeaf(const SPtr& symbol,
  // Specialization for nullptr_t.
  template <typename E>
  -const SyntaxTreeLeaf* CheckOptionalSymbolAsLeaf(const nullptr_t& symbol, E) {
  +const SyntaxTreeLeaf* CheckOptionalSymbolAsLeaf(const std::nullptr_t& symbol,
  + E) {
  return nullptr;
  }
  