GEE下载影像出错，Error: Can't get band number 0. Image has no bands. (Error code: 3)

Export.image.toDrive({
image: NDVI_Year_mean,
description: i+'year_mean',
region: roi,
scale:30,
maxPixels: 1e13,
folder: 'NN',
crs: "EPSG:4326",
})

}

报错：Error: Can't get band number 0. Image has no bands. (Error code: 3)