Use missingval instead of empty string for None values

tabulate/__init__.py

@@ -1623,7 +1623,7 @@ def _normalize_tabular_data(tabular_data, headers, showindex="default"):
     return rows, headers, headers_pad
 
 
-def _wrap_text_to_colwidths(list_of_lists, colwidths, numparses=True):
+def _wrap_text_to_colwidths(list_of_lists, colwidths, numparses=True, missingval=_DEFAULT_MISSINGVAL):
     if len(list_of_lists):
         num_cols = len(list_of_lists[0])
     else:
@@ -1646,7 +1646,7 @@ def _wrap_text_to_colwidths(list_of_lists, colwidths, numparses=True):
                 # explicit than just `str` of the object. Also doesn't work for
                 # custom floatfmt/intfmt, nor with any missing/blank cells.
                 casted_cell = (
-                    '' if cell is None else str(cell) if _isnumber(cell) else _type(cell, numparse)(cell)
+                    missingval if cell is None else str(cell) if _isnumber(cell) else _type(cell, numparse)(cell)
                 )
                 wrapped = [
                     "\n".join(wrapper.wrap(line))
@@ -2247,7 +2247,7 @@ def tabulate(
 
         numparses = _expand_numparse(disable_numparse, num_cols)
         list_of_lists = _wrap_text_to_colwidths(
-            list_of_lists, maxcolwidths, numparses=numparses
+            list_of_lists, maxcolwidths, numparses=numparses, missingval=missingval
         )
 
     if maxheadercolwidths is not None:
@@ -2261,7 +2261,7 @@ def tabulate(
 
         numparses = _expand_numparse(disable_numparse, num_cols)
         headers = _wrap_text_to_colwidths(
-            [headers], maxheadercolwidths, numparses=numparses
+            [headers], maxheadercolwidths, numparses=numparses, missingval=missingval
         )[0]
 
     # empty values in the first column of RST tables should be escaped (issue #82)

test/test_textwrapper.py

@@ -224,10 +224,7 @@ def test_wrap_datetime():
 
 def test_wrap_none_value():
     """TextWrapper: Show that None can be wrapped without crashing"""
-    data = [
-        ["First Entry", None],
-        ["Second Entry", None]
-    ]
+    data = [["First Entry", None], ["Second Entry", None]]
     headers = ["Title", "Value"]
     result = tabulate(data, headers=headers, tablefmt="grid", maxcolwidths=[7, 5])
 
@@ -244,3 +241,26 @@ def test_wrap_none_value():
     ]
     expected = "\n".join(expected)
     assert_equal(expected, result)
+
+
+def test_wrap_none_value_with_missingval():
+    """TextWrapper: Show that None can be wrapped without crashing and with a missing value"""
+    data = [["First Entry", None], ["Second Entry", None]]
+    headers = ["Title", "Value"]
+    result = tabulate(
+        data, headers=headers, tablefmt="grid", maxcolwidths=[7, 5], missingval="???"
+    )
+
+    expected = [
+        "+---------+---------+",
+        "| Title   | Value   |",
+        "+=========+=========+",
+        "| First   | ???     |",
+        "| Entry   |         |",
+        "+---------+---------+",
+        "| Second  | ???     |",
+        "| Entry   |         |",
+        "+---------+---------+",
+    ]
+    expected = "\n".join(expected)
+    assert_equal(expected, result)