With the FeatureReader transformer you can check for schema features. In Excel the worksheet is a schema. This way you can test if a sheet exists.

testforsheet2019.fmwt

The NoFeatureTester from FME Hub might help you.

Fantastic transformer! This is an excellent solution for these kinds of problems. What I like to do (if i'm expecting data to be written out) is to stick this python into a shutdown script. It's great for the FME Data Download service which has a habit of creating bad links.

#This shutdown script is used to catch unhandled excretions. This is the case when the workspace reports a 'Success', however, no features were written out. 

import fme
FeaturesWritten = str(fme.featuresWritten)
#print(FeaturesWritten)
status = fme.status
#print(status)
if status == 1 and FeaturesWritten == "{}":
    print("no data output - unhandled exception")
    raise Exception("unhandled exception")

It wont work if you are writing data with a feature writer, however, if working with normal writers it is a handy script.

I use a pythoncaller to create a feature if no input features exist - then send to a terminator/excel log etc.

Thank you for this tip, I keep it in mind but Takashi's solution is more simple and works exactly as I want. Have a good day !

Thank you once again Takashi, I couldn't expect that a Transformer would do the trick as there is no feature coming out from the reader but I tested and it works perfectly as I want.

Thanks, it's an interesting tip to use the UnmergedRequestor output from a FeatureMerger !

But NoFeatureTester is more simple and do the work perfectly ;)

Have a good day.

Thanks for this suggestion @ebygomm​ ! It too works well for my intention.