Program: 32586
Project: 32586
Buggy source:
private void invitations(DO todo){
  File file=new File(folder,"String_Node_Str");
  if (todo == DO.SAVE) {
    file.delete();
    Yamler pc=new Yamler(file);
    for (    Guild guild : GuildUtils.getGuilds()) {
      List<InvitationList.Invitation> invitationList=InvitationList.getInvitationsFrom(guild);
      for (      InvitationList.Invitation invitation : invitationList) {
        List<String> allyInvitations=new ArrayList<>();
        List<String> playerInvitations=new ArrayList<>();
        if (invitation.isToGuild()) {
          playerInvitations.add(invitation.getFor().toString());
        }
 else         if (invitation.isToAlly()) {
          allyInvitations.add(invitation.getFor().toString());
        }
        pc.set(invitation.getFrom().toString() + "String_Node_Str",allyInvitations);
        pc.set(invitation.getFrom().toString() + "String_Node_Str",playerInvitations);
      }
    }
    pc.save();
  }
 else   if (todo == DO.LOAD) {
    if (!file.exists()) {
      return;
    }
    Yamler pc=new Yamler(file);
    for (    String key : pc.getKeys(false)) {
      Guild guild=Guild.get(UUID.fromString(key));
      if (guild != null) {
        List<String> allyInvitations=pc.getStringList(key + "String_Node_Str");
        List<String> playerInvitations=pc.getStringList(key + "String_Node_Str");
        for (        String ally : allyInvitations) {
          Guild allyGuild=Guild.get(UUID.fromString(ally));
          if (allyGuild != null) {
            InvitationList.createInvitation(guild,allyGuild);
          }
        }
        for (        String player : playerInvitations) {
          InvitationList.createInvitation(guild,UUID.fromString(player));
        }
      }
    }
  }
}

Fixed version (ground truth):
private void invitations(DO todo){
  File file=new File(folder,"String_Node_Str");
  if (todo == DO.SAVE) {
    file.delete();
    Yamler pc=new Yamler(file);
    for (    Guild guild : GuildUtils.getGuilds()) {
      List<InvitationList.Invitation> invitationList=InvitationList.getInvitationsFrom(guild);
      for (      InvitationList.Invitation invitation : invitationList) {
        List<String> allyInvitations=new ArrayList<>();
        List<String> playerInvitations=new ArrayList<>();
        if (invitation.isToGuild()) {
          playerInvitations.add(invitation.getFor().toString());
        }
 else         if (invitation.isToAlly()) {
          allyInvitations.add(invitation.getFor().toString());
        }
        pc.set(invitation.getFrom().toString() + "String_Node_Str",allyInvitations);
        pc.set(invitation.getFrom().toString() + "String_Node_Str",playerInvitations);
      }
    }
    pc.save();
  }
 else   if (todo == DO.LOAD) {
    if (!file.exists()) {
      return;
    }
    Yamler pc=new Yamler(file);
    for (    String key : pc.getKeys(false)) {
      Guild guild=GuildUtils.getByUUID(UUID.fromString(key));
      if (guild != null) {
        List<String> allyInvitations=pc.getStringList(key + "String_Node_Str");
        List<String> playerInvitations=pc.getStringList(key + "String_Node_Str");
        for (        String ally : allyInvitations) {
          Guild allyGuild=GuildUtils.getByUUID(UUID.fromString(ally));
          if (allyGuild != null) {
            InvitationList.createInvitation(guild,allyGuild);
          }
        }
        for (        String player : playerInvitations) {
          InvitationList.createInvitation(guild,UUID.fromString(player));
        }
      }
    }
  }
}