Losing label assign causes gauge push failed.

[slow-groovin]

NewGauge step with multiple labels

io::prometheus::NewGauge name=sample_count help='' labels=path,path2

set one and push

#record1
sample_count -path=/path/any set 1 
#record2
sample_count -path=/path/any -path2=/path/any2 set 2 
#io::prometheus::PushAdd  ......

result

the first record will fail to be pushed into the gateway
the second record will suc