def [](key)
      bmp_def = _get_definition key
      bmp     = @values[bmp_def.bmp]
      bmp ? bmp.value : nil
    end
def [](key)
      bmp_def = _get_definition key
      bmp     = @values[bmp_def.bmp]
      bmp ? bmp.value : nil
    end
Retrieve the decoded value of the contents of a bitmap
 described either by the bitmap number or name.

 ===Example

    mes = BlaBlaMessage.parse someMessageBytes
    mes[2] # bmp 2 is generally the PAN
    mes["Primary Account Number"] # if thats what you called the field in Message.bmp.