Unable to push to cloned empty repository using Java API (GitCommandBuilderFactory)

[Severin]

I'm not able to push files using the Java API of bitbucket. The following code shows my attempt to add commits to a new and empty repository:

GitCommandBuilderFactory builderFactory; // imported with component-import

// create working directory (outside repository)
Path workTree = createWorkTree(repository);

// cloning repository to working directory
builderFactory.builder(repository)
.clone()
.normal()
.directory(workTree)
.origin(repository)
.build()
.call();

// create the file in the working directory
createFile(file, content);

// add the file
builderFactory.builder(repository)
.add()
.all(true)
.workDir(workTree)
.build()
.call();

// commit
builderFactory.builder(repository)
.commit()
.workDir(workTree)
.message(String.format("Added file %s", filename))
.author(Objects.requireNonNull(authenticationContext.getCurrentUser()))
.build()
.call();

// push - here is where the error occurs
builderFactory.builder(repository)
.push()
.workDir(workTree)
.build(new SingleLineOutputHandler())
.call();

After executing the above code snippet, I get the following error:

[INFO] com.atlassian.bitbucket.scm.CommandFailedException: 'C:\Program Files\Git\cmd\git.exe push' exited with code 1 saying: remote: hooks/pre-receive: line 9: /c/Users/$username/Code/$projectname/target/bitbucket/home/shared/data/repositories/14/hooks/pre-receive.d: Is a directory 
[INFO] remote: hooks/pre-receive: line 9: exec: /c/Users/$username/Code/$projectname/target/bitbucket/home/shared/data/repositories/14/hooks/pre-receive.d: cannot execute: Is a directory 
[INFO] To C:\Users\$username\Code\$projectname\target\bitbucket\home\shared\data\repositories\14
[INFO] ! [remote rejected] master -> master (pre-receive hook declined)
[INFO] error: failed to push some refs to 'C:\Users\$username\Code\$projectname\target\bitbucket\home\shared\data\repositories\14'

I'm able to commit some files using the 'EditFileCommand,' but this does not fit my needs, as I need to modify some environment variables in the commit. Does anybody have an idea?