How to use the nem2-sdk.PlainMessage.create function in nem2-sdk

public update(fileContent: string, hashFunction: HashFunction): TransferTransaction {
    this.hash = hashFunction.nonSignedHashing(fileContent);
    const creationTransaction = TransferTransaction.create(
      Deadline.create(),
      this.sinkAddress,
      [
        new Mosaic(new NamespaceId('nem.xem'), UInt64.fromUint(10)),
      ],
      PlainMessage.create(this.hash),
      this.sinkAddress.networkType,
    );
    return creationTransaction;
  }

public update(rawData: string, destAddress?: Address): TransferTransaction {
    const plainMessage = PlainMessage.create(rawData);

    const creationTransaction = TransferTransaction.create(
      Deadline.create(),
      destAddress || this.publicAccount.address,
      [],
      plainMessage,
      this.publicAccount.address.networkType,
    );

    return creationTransaction;
  }