prevent max over empty iterator

Author: huettenhain

refinery/units/formats/office/docmeta.py

@@ -84,4 +84,6 @@ def interpret(value: str | dict):
             for name, value in contents.items():
                 contents[name] = interpret(value)
 
+        if not result:
+            return None
         yield from ppjson(tabular=self.args.tabular)._pretty_output(result)