GroovyScript doesn't work correct on Jenkins Master

Question

I am running the following Groovy script which works perfect from the compiler & Jenkins ( if it runs a slave /node)

Because I want to run the script the "This project is parameterised" I noticed Jenkins is always running.

I Use the following Script:

// setup SSH connection:
sshString = "ssh -T -i keyfile -p 22 [email protected] "
cmdLine = "/appl/test/script.sh"
conString = sshString + cmdLine

// execute command

def proc            = conString.execute()
def outputStream    = new StringBuffer()

proc.waitForProcessOutput(outputStream, System.out)

output =  (outputStream .toString())

println(output)

On the slave I get the result of the shell script, on the master the result is NULL.

What am I doing wrong