Program: 80917
Project: 80917
Buggy source:
public String getMainGroup(IPlayer player){
  String bpgroup=null;
  Plugin p=ProxyServer.getInstance().getPluginManager().getPlugin("String_Node_Str");
  if (p != null) {
    BungeePerms bp=BungeePerms.getInstance();
    try {
      User user=bp.getPermissionsManager().getUser(player.getName());
      Group mainGroup=null;
      if (user != null) {
        mainGroup=bp.getPermissionsManager().getMainGroup(user);
      }
      if (mainGroup == null) {
        if (!bp.getPermissionsManager().getDefaultGroups().isEmpty()) {
          mainGroup=bp.getPermissionsManager().getDefaultGroups().get(0);
          for (int i=1; i < bp.getPermissionsManager().getDefaultGroups().size(); ++i) {
            if (bp.getPermissionsManager().getDefaultGroups().get(i).getWeight() < mainGroup.getWeight()) {
              mainGroup=bp.getPermissionsManager().getDefaultGroups().get(i);
            }
          }
        }
      }
      if (mainGroup != null) {
        bpgroup=mainGroup.getName();
      }
    }
 catch (    NullPointerException ex) {
      BungeeTabListPlus.getInstance().getLogger().log(Level.SEVERE,"String_Node_Str",ex);
    }
catch (    Throwable th) {
      BungeeTabListPlus.getInstance().reportError(th);
    }
  }
  Optional<String> vgroup=plugin.getBridge().getPlayerInformation(player,Values.Player.Vault.PermissionGroup);
  String bgroup=null;
  Collection<String> groups=plugin.getProxy().getConfigurationAdapter().getGroups(player.getName());
  if (groups.size() == 1) {
    bgroup=groups.iterator().next();
  }
  for (  String group : groups) {
    if (!group.equals("String_Node_Str")) {
      bgroup=group;
      break;
    }
  }
  if (bgroup == null) {
    bgroup="String_Node_Str";
  }
  String mode=plugin.getConfigManager().getMainConfig().permissionSource;
  if (mode.equalsIgnoreCase("String_Node_Str")) {
    return bpgroup != null ? bpgroup : "String_Node_Str";
  }
 else   if (mode.equalsIgnoreCase("String_Node_Str")) {
    return vgroup.isPresent() ? vgroup.get() : "String_Node_Str";
  }
 else   if (mode.equalsIgnoreCase("String_Node_Str")) {
    return bgroup;
  }
  if (bpgroup != null) {
    return bpgroup;
  }
  if (vgroup.isPresent()) {
    return vgroup.get();
  }
  return bgroup;
}

Fixed version (ground truth):
public String getMainGroup(IPlayer player){
  String bpgroup=null;
  Plugin p=ProxyServer.getInstance().getPluginManager().getPlugin("String_Node_Str");
  if (p != null) {
    BungeePerms bp=BungeePerms.getInstance();
    try {
      PermissionsManager pm=bp.getPermissionsManager();
      if (pm != null) {
        User user=pm.getUser(player.getName());
        Group mainGroup=null;
        if (user != null) {
          mainGroup=pm.getMainGroup(user);
        }
        if (mainGroup == null) {
          if (!pm.getDefaultGroups().isEmpty()) {
            mainGroup=pm.getDefaultGroups().get(0);
            for (int i=1; i < pm.getDefaultGroups().size(); ++i) {
              if (pm.getDefaultGroups().get(i).getWeight() < mainGroup.getWeight()) {
                mainGroup=pm.getDefaultGroups().get(i);
              }
            }
          }
        }
        if (mainGroup != null) {
          bpgroup=mainGroup.getName();
        }
      }
    }
 catch (    NullPointerException ex) {
      BungeeTabListPlus.getInstance().getLogger().log(Level.SEVERE,"String_Node_Str",ex);
    }
catch (    Throwable th) {
      BungeeTabListPlus.getInstance().reportError(th);
    }
  }
  Optional<String> vgroup=plugin.getBridge().getPlayerInformation(player,Values.Player.Vault.PermissionGroup);
  String bgroup=null;
  Collection<String> groups=plugin.getProxy().getConfigurationAdapter().getGroups(player.getName());
  if (groups.size() == 1) {
    bgroup=groups.iterator().next();
  }
  for (  String group : groups) {
    if (!group.equals("String_Node_Str")) {
      bgroup=group;
      break;
    }
  }
  if (bgroup == null) {
    bgroup="String_Node_Str";
  }
  String mode=plugin.getConfigManager().getMainConfig().permissionSource;
  if (mode.equalsIgnoreCase("String_Node_Str")) {
    return bpgroup != null ? bpgroup : "String_Node_Str";
  }
 else   if (mode.equalsIgnoreCase("String_Node_Str")) {
    return vgroup.isPresent() ? vgroup.get() : "String_Node_Str";
  }
 else   if (mode.equalsIgnoreCase("String_Node_Str")) {
    return bgroup;
  }
  if (bpgroup != null) {
    return bpgroup;
  }
  if (vgroup.isPresent()) {
    return vgroup.get();
  }
  return bgroup;
}