support null-serialization in list-csv conversions

HISTORY.md

@@ -8,9 +8,13 @@
 * **Notable Changes:**
     * when creating a costume from pen trails (raster or vector) make its rotation center the position of the sprite
 * **Notable Fixes:**
+    * support null-serialization in list-csv conversions
 * **Translation Updates:**
     * German
 
+### 2019-12-08
+* lists: support null-serialization in list-csv conversions
+
 ### 2019-12-07
 * threads: turn "log pen trails" off when loading or creating a new project
 

snap.html

@@ -11,7 +11,7 @@
         <script type="text/javascript" src="src/objects.js?version=2019-12-05"></script>
         <script type="text/javascript" src="src/gui.js?version=2019-12-07"></script>
         <script type="text/javascript" src="src/paint.js?version=2019-06-27"></script>
-        <script type="text/javascript" src="src/lists.js?version=2019-11-15"></script>
+        <script type="text/javascript" src="src/lists.js?version=2019-12-08"></script>
         <script type="text/javascript" src="src/byob.js?version=2019-07-12"></script>
         <script type="text/javascript" src="src/tables.js?version=2019-06-27"></script>
         <script type="text/javascript" src="src/symbols.js?version=2019-06-27"></script>

src/lists.js

@@ -62,7 +62,7 @@ CellMorph, ArrowMorph, MenuMorph, snapEquals, Morph, isNil, localize, isString,
 MorphicPreferences, TableDialogMorph, SpriteBubbleMorph, SpeechBubbleMorph,
 TableFrameMorph, TableMorph, Variable, isSnapObject, Costume, contains*/
 
-modules.lists = '2019-November-15';
+modules.lists = '2019-December-08';
 
 var List;
 var ListWatcherMorph;
@@ -425,7 +425,7 @@ List.prototype.asCSV = function () {
         rows = [];
     
     function encodeCell(atomicValue) {
-        var string = atomicValue.toString(),
+        var string = isNil(atomicValue) ? '' : atomicValue.toString(),
             cell;
         if (string.indexOf('\"') ===  -1 &&
                 (string.indexOf('\n') === -1) &&