How to read the content of a file into Byte and write Byte to a file?

public static byte[] ReadFileToByte(string fileName)
{
    byte[] data = null; 

    // Check whether the image file exists or not
    if (fileName == null || fileName.Length <= 0 || !File.Exists(fileName)) 
    {
        return data;
    } 

    try
    {
        // Open the image file
        FileStream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
        BinaryReader br = new BinaryReader(fs);
        // Read the image into the byte variable
        data = br.ReadBytes((int)fs.Length);

        br.Close();
        fs.Close();
    }
    catch(Exception ex)
    {
        ...
    } 

    return data;
} 

/// <summary>
/// Write the content of a byte variable into a file
/// </summary>
/// <param name="data">The byte variable</param>
/// <param name="fileName">The name of the target file</param>
public static void WriteByteToFile(byte[] data, string fileName)
{
    // Check whether there is data in the byte variable
    if ((data==null) || (data.Length<=0)) 
    {
        return;
    } 

    if (fileName==null||fileName.Trim()==String.Empty)
    {
        return;
    }
    try
    {
        // Open the target file. If it doesn't exist, create it.
        FileStream fs = new FileStream(fileName, FileMode.OpenOrCreate, FileAccess.Write);
        BinaryWriter bw = new BinaryWriter(fs);
        // Write the content of the byte variable into the file
        bw.Write(data);

        bw.Flush();
        bw.Close();
        fs.Close(); 

    }
    catch(Exception ex)
    {
        ...
    } 
}