TensorRT 5.1.2 - trtexec error: UffParser: Unsupported number of graph 0

Input parameter seems to be mandatory. Try this:

./trtexec --uff=/workspace/tensorrt/python/data/resnet50/resnet50-infer-5.uff --batch=1 --output=GPU_0/tower_0/Softmax --uffInput=input,3,224,224