Merge pull request #4980 from jlp765/tostring

Add nill value handling for seq/sets to system.CollectionToString()

lib/system.nim

@@ -2334,7 +2334,8 @@ proc collectionToString[T: set | seq](x: T, b, e: string): string =
   var firstElement = true
   for value in items(x):
     if not firstElement: result.add(", ")
-    result.add($value)
+    if value.isNil: result.add "nil"
+    else: result.add($value)
     firstElement = false
   result.add(e)
 

tests/stdlib/tnilecho.nim

@@ -0,0 +1,2 @@
+var x = @["1", nil, "3"]
+doAssert $x == "@[1, nil, 3]"