diff -r f1c5358f0d65 -r 90b9a7e06c2c mercurial/logcmdutil.py
--- a/mercurial/logcmdutil.py	Sat Oct 05 23:04:45 2019 -0400
+++ b/mercurial/logcmdutil.py	Sat Oct 05 23:20:35 2019 -0400
@@ -617,9 +617,6 @@
                 mapfile = mapname
         return templatespec(None, mapfile)
 
-    if not tmpl:
-        return templatespec(None, None)
-
     return formatter.lookuptemplate(ui, b'changeset', tmpl)
 
 
@@ -642,12 +639,15 @@
     regular display via changesetprinter() is done.
     """
     postargs = (differ, opts, buffered)
-    if opts.get(b'template') in {b'cbor', b'json'}:
+    spec = _lookuptemplate(ui, opts.get(b'template'), opts.get(b'style'))
+
+    # machine-readable formats have slightly different keyword set than
+    # plain templates, which are handled by changesetformatter.
+    # note that {b'pickle', b'debug'} can also be added to the list if needed.
+    if spec.ref in {b'cbor', b'json'}:
         fm = ui.formatter(b'log', opts)
         return changesetformatter(ui, repo, fm, *postargs)
 
-    spec = _lookuptemplate(ui, opts.get(b'template'), opts.get(b'style'))
-
     if not spec.ref and not spec.tmpl and not spec.mapfile:
         return changesetprinter(ui, repo, *postargs)