Reinsert type check in merge loop.

Author: alexandermorgan

pvlib/bifacial.py

@@ -182,6 +182,7 @@ def merge(reports):
         report = reports[0]
         keys_report = list(report.keys())
         for other_report in reports[1:]:  # loop won't run if len(reports) < 2
-            for key in keys_report:
-                report[key] += other_report[key]
+            if isinstance(other_report, dict):
+                for key in keys_report:
+                    report[key] += other_report[key]
         return report