Doh, Jenkins says "java.io.IOException: Is a directory"

I'm using Jenkins to build a container image, using a Jenkinsfile hosted in a GitHub project, and was hitting this each and every time I ran my build: - 

java.io.IOException: Is a directory
at sun.nio.ch.FileDispatcherImpl.read0(Native Method)
at sun.nio.ch.FileDispatcherImpl.read(FileDispatcherImpl.java:46)
at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223)
at sun.nio.ch.IOUtil.read(IOUtil.java:197)
at sun.nio.ch.FileChannelImpl.read(FileChannelImpl.java:159)
at sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:65)
at sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:109)
at sun.nio.ch.ChannelInputStream.read(ChannelInputStream.java:103)
at java.nio.file.Files.read(Files.java:3105)
at java.nio.file.Files.readAllBytes(Files.java:3158)
at hudson.FilePath$ReadToString.invoke(FilePath.java:2286)
at hudson.FilePath$ReadToString.invoke(FilePath.java:2282)
at hudson.FilePath.act(FilePath.java:1165)
at hudson.FilePath.act(FilePath.java:1148)
at hudson.FilePath.readToString(FilePath.java:2280)
at org.jenkinsci.plugins.workflow.cps.CpsScmFlowDefinition.create(CpsScmFlowDefinition.java:183)
at org.jenkinsci.plugins.workflow.cps.CpsScmFlowDefinition.create(CpsScmFlowDefinition.java:68)
at org.jenkinsci.plugins.workflow.job.WorkflowRun.run(WorkflowRun.java:309)
at hudson.model.ResourceController.execute(ResourceController.java:97)
at hudson.model.Executor.run(Executor.java:429)
Finished: FAILURE

Like a fool, I dug into the actual Jenkinsfile, looking at the Groovy formatting and conventions, including the embedded Bash script ...

And couldn't find the root cause ...

And then I compared and contrasted my new Jenkins build job with one that actually worked ...

And then realised that it was a PEBCAK 

Yep, I'd specified the Script Path quite correctly BUT hadn't actually specified the name of the Jenkinsfile ...

Ordinarily, that'd probably be OK, assuming that Jenkins assumes that all Jenkinsfiles are called Jenkinsfile.

But... in my case, the Jenkinsfile is called ... build_push_etcd_operator_Jenkinsfile.

In other words, the error message: -

java.io.IOException: Is a directory

was 100% correct; /etcd-operator/ is definitely a directory, not a file ....

Once I updated the path: -

all was good 😅

Can you say "Doofus" ?  I bet you can .....