From ea88bfc8af1457eedeabde31ed153cb7e255a0fe Mon Sep 17 00:00:00 2001
From: Tom Keffer <tkeffer@gmail.com>
Date: Fri, 15 May 2020 17:42:00 -0700
Subject: [PATCH] Test for None_string that cannot be converted using ASCII
 codec.

---
 bin/weewx/tests/test_units.py | 15 ++++++++++++++-
 bin/weewx/units.py            |  6 +++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/bin/weewx/tests/test_units.py b/bin/weewx/tests/test_units.py
index a9d48bdf..ff8e62f1 100644
--- a/bin/weewx/tests/test_units.py
+++ b/bin/weewx/tests/test_units.py
@@ -149,7 +149,20 @@ class ValueHelperTest(unittest.TestCase):
         self.assertEqual(six.text_type(vh), u"68.0°F")
         self.assertEqual(six.text_type(vh.degree_F), u"68.0°F")
         self.assertEqual(six.text_type(vh.degree_C), u"20.0°C")
-        
+
+        # Using .format() interface
+        self.assertEqual(vh.format(), u"68.0°F")
+        self.assertEqual(vh.format("T=%.3f", add_label=False), u"T=68.010")
+
+        # Test None_string
+        value_t = (None, "degree_F", "group_temperature")
+        vh = weewx.units.ValueHelper(value_t)
+        self.assertEqual(vh.format(None_string='foo'), u'foo')
+        self.assertTrue(isinstance(vh.format(None_string='foo'), six.text_type))
+        # This one cannot be done with ASCII codec:
+        self.assertEqual(vh.format(None_string=u'unknown °F'), u'unknown °F')
+        self.assertTrue(isinstance(vh.format(None_string=u'unknown °F'), six.text_type))
+
     def testFormattingWithConversion(self):
         value_t = (68.01, "degree_F", "group_temperature")
         c_m = weewx.units.Converter(weewx.units.MetricUnits)
diff --git a/bin/weewx/units.py b/bin/weewx/units.py
index 1fadf297..adea4197 100644
--- a/bin/weewx/units.py
+++ b/bin/weewx/units.py
@@ -744,7 +744,11 @@ class Formatter(object):
                 val_str = self.unit_format_dict.get('NONE', u'N/A')
             else:
                 # Make sure the "None_string" is, in fact, a string
-                val_str = str(None_string)
+                if isinstance(None_string, six.string_types):
+                    val_str = None_string
+                else:
+                    # Coerce to a string.
+                    val_str = str(None_string)
             addLabel = False
         elif val_t[1] == "unix_epoch":
             # Different formatting routines are used if the value is a time.