diff --git a/src/cutadapt/report.py b/src/cutadapt/report.py
index 2b47d8ed..da1dda32 100644
--- a/src/cutadapt/report.py
+++ b/src/cutadapt/report.py
@@ -280,7 +280,7 @@ def _adapter_statistics_as_json(
                     error_rate=end_statistics.max_error_rate,
                 ).lengths()
             else:
-                eranges = None
+                eranges = []
             base_stats = AdjacentBaseStatistics(end_statistics.adjacent_bases)
             trimmed_lengths = [
                 make_line(