src/Transaction/TransactionBuilder.php
public function addMergeOperation($destinationAccountId, $sourceAccountId = null)
    {
        if ($destinationAccountId instanceof Keypair) {
            $destinationAccountId = $destinationAccountId->getPublicKey();
        }

        return $this->addOperation(new AccountMergeOp($destinationAccountId, $sourceAccountId));
    }
public function addMergeOperation($destinationAccountId, $sourceAccountId = null)
    {
        if ($destinationAccountId instanceof Keypair) {
            $destinationAccountId = $destinationAccountId->getPublicKey();
        }

        return $this->addOperation(new AccountMergeOp($destinationAccountId, $sourceAccountId));
    }
Adds an operation to merge the balance of the source account to $destinationAccountId
@param      $destinationAccountId
@param null $sourceAccountId
@return TransactionBuilder