updated docs, Util functions and fixed last issues

src/classes/util/DcsUtil.lua

@@ -632,6 +632,12 @@ do     -- INIT DCS_UTIL
     ---@field b number
     ---@field a number
 
+    local drawID = 4210
+
+    function DCS_UTIL.GetNextDrawID()
+        drawID = drawID + 1
+        return drawID
+    end
 
     ---@param groupID number
     ---@param text string
@@ -677,6 +683,10 @@ do     -- INIT DCS_UTIL
     ---@param drawID number
     ---@param fillColor DrawColor
     function DCS_UTIL.SetFillColor(drawID, fillColor)
+        if fillColor == nil then
+            return
+        end
+
         local lineColorMapped = {
             fillColor.r or 0,
             fillColor.g or 0,