skip empty files

performanceDb/src/main/java/org/lucares/performance/db/PdbFileIterator.java

@@ -34,14 +34,19 @@ public class PdbFileIterator implements Iterator<Entry>, AutoCloseable {
 			if (reader == null) {
 				return null;
 			}
-			final Entry entry = reader.readNullableEntry();
+			Entry entry = reader.readNullableEntry();
 
-			if (entry == null) {
+			while (entry == null) {
 				nextFile();
 				if (reader == null) {
 					return null;
 				} else {
-					return reader.readEntry().orElse(null);
+					entry = reader.readEntry().orElse(null);
+					// A reader might return null, for a newly opened reader,
+					// if the file was created, but nothing has been written to
+					// disk yet.
+					// This might happen, because of buffering, or when an ingestion
+					// was cancelled.
 				}
 			}