Repair and test logic to avoid printing None strings

tests/test_subreddit.py

@@ -870,6 +870,12 @@ def test_subreddit_page__draw_item_format(terminal, subreddit_page):
     assert not terminal.add_line.called
     terminal.add_line.reset_mock()
 
+    # add_line shouldn't be called if the string field is none
+    subreddit_page.format = [(None, lambda data: None, False)]
+    subreddit_page._draw_item_format(win, None, None, 0)
+
+    assert not terminal.add_line.called
+
     # Check for newline handling and attribute reusing in the call of a null
     # attribute
     subreddit_page.format = [("string", lambda data: terminal.attr("Link"), True),

tuir/subreddit_page.py

@@ -391,7 +391,7 @@ class SubredditPage(Page):
         for get_data, get_attr, first in self.format:
             # add_line wants strings, make sure we give it strings
             if callable(get_data):
-                string = str(get_data(data))
+                string = get_data(data)
             else:
                 # Start writing to the next line if we hit a newline
                 if get_data == "\n":
@@ -399,17 +399,20 @@ class SubredditPage(Page):
                     continue
 
                 # Otherwise, proceed on the same line
-                string = str(get_data)
+                string = get_data
+
+            # Don't try to write None strings to the screen. This happens in
+            # places like user pages, where data['comments'] is None
+            if not string and first is False:
+                continue
+
+            string = str(string)
 
             # We only want to print a maximum of one line of data
             # TODO - support line wrapping
             string = string.split('\n')[0]
 
-            # Don't try to write null strings to the screen. This happens in
-            # places like user pages, where data['comments'] is None
-            if string is None:
-                continue
-            elif string is ' ':
+            if string is ' ':
                 # Make sure spaces aren't treated like normal strings and print
                 # them to the window this way. This ensures they won't be drawn
                 # with an attribute.