First off, you shouldn't add $ when you're outside of strings ($class in your first function being an exception), so it should be:
def doCopyMibArtefactsHere(projectName) {
step ([
$class: 'CopyArtifact',
projectName: projectName,
filter: '**/**.mib',
fingerprintArtifacts: true,
flatten: true
]);
}
def BuildAndCopyMibsHere(projectName, params) {
build job: project, parameters: params
doCopyMibArtefactsHere(projectName)
}
...
Now, as for your problem; the second function takes two arguments while you're only supplying one argument at the call. Either you have to supply two arguments at the call:
...
node {
stage('Prepare Mib'){
BuildAndCopyMibsHere('project1', null)
}
}
... or you need to add a default value to the functions' second argument:
def BuildAndCopyMibsHere(projectName, params = null) {
build job: project, parameters: params
doCopyMibArtefactsHere($projectName)
}