fix(map) setdefault will now honor a 'false' value

lua/pl/Map.lua

@@ -55,10 +55,17 @@ function Map:items()
     return ls
 end
 
---- Will return the existing value, or if it doesn't exist it will set
--- a default value and return it.
-function Map:setdefault(key, defaultval)
-   return self[key] or self:set(key,defaultval) or defaultval
+--- set a value in the map if it doesn't exist yet.
+-- @param key the key
+-- @param default value to set
+-- @return the value stored in the map (existing value, or the new value)
+function Map:setdefault(key, default)
+    local val = self[key]
+    if val ~= nil then
+        return val
+    end
+    self:set(key,default)
+   return default
 end
 
 --- size of map.

tests/test-map.lua

@@ -78,6 +78,9 @@ asserteq(
       {'gamma', 3},
     }
 )
+v = m:set("alpha", false)
+v = m:setdefault("alpha", true)   -- falsy value should not be altered
+asserteq(false, m:get("alpha"))