add mapNotNull to ObjIterable with documentation

lynglib/src/commonMain/kotlin/net/sergeych/lyng/obj/ObjIterable.kt

@@ -158,6 +158,23 @@ val ObjIterable by lazy {
             ObjList(result)
         }
 
+        addFnDoc(
+            name = "mapNotNull",
+            doc = "Transform elements by applying the given lambda unless it returns null.",
+            params = listOf(ParamDoc("transform")),
+            returns = type("lyng.List"),
+            isOpen = true,
+            moduleName = "lyng.stdlib"
+        ) {
+            val fn = requiredArg<Statement>(0)
+            val result = mutableListOf<Obj>()
+            thisObj.toFlow(this).collect {
+                val transformed = fn.call(this, it)
+                if( transformed != ObjNull) result += transformed
+            }
+            ObjList(result)
+        }
+
         addFnDoc(
             name = "take",
             doc = "Take the first N elements and return them as a list.",