Why does Spock think my Data Provider has no data? - groovy

Question

I just wrote my own data Provider, which should read a file in chunks and provides it to my spock specification.
While debugging the next() method returns a proper batch and the hasNext() returns false if the reader can not read any more lines.
But I get this exception: SpockExecutionException: Data provider has no data
Here is my Provider and my feature
class DumpProvider implements Iterable<ArrayList<String>> {
private File fileHandle
private BufferedReader fileReader
private ArrayList<String> currentBatch = new ArrayList<String>()
private int chunksize
private boolean hasNext = true
DumpProvider(String pathToFile, int chunksize) {
this.chunksize = chunksize
this.fileHandle = new File(pathToFile)
this.fileReader = this.fileHandle.newReader()
}
#Override
Iterator iterator() {
new Iterator<ArrayList<String>>() {
#Override
boolean hasNext() {
if (hasNext) {
String nextLine = fileReader.readLine()
if (nextLine != null) {
currentBatch.push(nextLine)
} else {
hasNext = false
fileReader.close()
fileHandle = null
}
}
return hasNext
}
#Override
ArrayList<String> next() {
(chunksize - currentBatch.size()).times {
String line = fileReader.readLine()
if (line != null) {
currentBatch.push(line)
}
}
def batch = new ArrayList<String>(currentBatch)
currentBatch = new ArrayList<String>()
return batch
}
#Override
void remove() {
throw new UnsupportedOperationException();
}
}
}
}
Spock Feature
def "small import"() {
when:
println 'test'
println profileJSONStrings
connector.insertMultiple(profileJSONStrings as ArrayList<String>)
then:
println "hello"
where:
profileJSONStrings << dataProvider
}