Async.waterfall: Callback already was called?

I know this is a topic that has been brought up here before, but I'm using async.waterfall with rethinkdb and I'm getting Error: Callback was already called. The odd part is that even though it throws that error and crashes the app, it still will create the database and tables I need. I have read a few other post with answers like NodeJS Async: Callback already called? or Using async.waterfall, but I can't seem to get anywhere. My console also tells me the error is at db.js:40:9, but I'm new to Node and just not sure what it wants with the callbacks. What am I doing wrong? Do I need to nest my callbacks here? The code I am using is posted below. Any help I can get here is greatly appreciated and if need be I can post other relevant code. Thanks guys.

db.js:

exports.setDatabaseAndTables = function() {
    async.waterfall([
    function connect(callback) {
      r.connect(config.rethinkdb, callback);
    },
    function createDatabase(connection, callback) {
      // Create the database if needed.
      r.dbList().contains(config.rethinkdb.db).do(function(containsDb) {
        return r.branch(
          containsDb,
          {created: 0},
          r.dbCreate(config.rethinkdb.db)
        );
      }).run(connection, function(err) {
        callback(err, connection);
      });
    },
    function createTable(connection, callback) {
      // Create the tables if needed.
      r.tableList().contains('todos').do(function(containsTable) {
        return r.branch(
          containsTable,
          {created: 0},
          r.tableCreate('todos')
        );
      }).run(connection, function(err) {
        callback(err, connection);
      });
      r.tableList().contains('users').do(function(containsTable) {
        return r.branch(
          containsTable,
          {created: 0},
          r.tableCreate('users')
        );
      }).run(connection, function(err) {
        callback(err, connection);
      });
    },
    function createIndex(connection, callback) {
      // Create the indexes if needed.
      r.table('todos').indexList().contains('createdAt').do(function(hasIndex) {
        return r.branch(
          hasIndex,
          {created: 0},
          r.table('todos').indexCreate('createdAt')
        );
      }).run(connection, function(err) {
        callback(err, connection);
      });
      r.table('users').indexList().contains('createdAt').do(function(hasIndex) {
        return r.branch(
          hasIndex,
          {created: 0},
          r.table('users').indexCreate('createdAt')
        );
      }).run(connection, function(err) {
        callback(err, connection);
      });
    },
    function waitForIndex(connection, callback) {
      // Wait for the index to be ready.
      r.table('todos').indexWait('createdAt').run(connection, function(err, result) {
        callback(err, connection);
      });
      r.table('users').indexWait('createdAt').run(connection, function(err, result) {
        callback(err, connection);
      });
    }
  ], function(err, connection) {
    if(err) {
      console.error(err);
      process.exit(1);
      return;
    }
  });
};

via Daniel D