warning in midi

[MING TSANG]

Hi, lily users:

I added crescendo to a song and I got the warning message. The PDF output correctly.  What can I do to eliminated the warning message.

Thanks for your help.

Ming

C:/Users/Gladys Tsang/Documents/My Dropbox/Lyndon/LiLy/this-is-the-day/this-is-the-day_transpose-AG_ED.ly:24:19: warning: (De)crescendo with unspecified starting volume in MIDI.

r2 \times 2/3{ a4

^\< d4 e4^\! } | fs2.^\f e8 d8 | e4.^- a,8 a2~^\> | a4^\! fs4^\mf b4 b4 | \bk % 17-20