make the vccexe helper tool compile again

tools/vccenv/vccenv.nim

@@ -19,7 +19,7 @@ proc getVsComnToolsPath*(): TaintedString =
       return vsComnToolsEnvVal
 
 proc getVccEnv*(platform: string, windowsStoreSdk: bool = false,
-                sdkVersion: string = nil): StringTableRef =
+                sdkVersion: string = ""): StringTableRef =
   var comSpecCommandString = getEnv comSpecEnvKey
   if comSpecCommandString.len == 0:
     comSpecCommandString = "cmd"

tools/vccenv/vccexe.nim

@@ -5,14 +5,14 @@ when defined(release):
 else:
   let vccOptions = {poEchoCmd, poParentStreams}
 
-const 
+const
   platformPrefix = "--platform"
   winstorePrefix = "--winstore"
   sdkversionPrefix = "--sdkversion"
 
   platformSepIdx = platformPrefix.len
   sdkversionSepIdx = sdkversionPrefix.len
-  
+
   HelpText = """
 +-----------------------------------------------------------------+
 |         Microsoft C/C++ compiler wrapper for Nim                |
@@ -26,7 +26,7 @@ Options:
                       <arch>: x86 | amd64 | arm | x86_amd64 | x86_arm | amd64_x86 | amd64_arm
   --winstore          Use Windows Store (rather than desktop) development tools
   --sdkversion:<v>    Use a specific Windows SDK version:
-                      <v> is either the full Windows 10 SDK version number or 
+                      <v> is either the full Windows 10 SDK version number or
                       "8.1" to use the windows 8.1 SDK
 
 Other command line arguments are passed on to the
@@ -34,8 +34,8 @@ Microsoft C/C++ compiler for the specified SDK toolset
 """
 
 when isMainModule:
-  var platformArg: string = nil
-  var sdkVersionArg: string = nil
+  var platformArg: string = ""
+  var sdkVersionArg: string = ""
   var storeArg: bool = false
 
   var clArgs: seq[TaintedString] = @[]
@@ -54,7 +54,7 @@ when isMainModule:
         echo HelpText
       clArgs.add(wargv)
 
-  var vccEnvStrTab = getVccEnv(platformArg, storeArg, sdkVersionArg)  
+  var vccEnvStrTab = getVccEnv(platformArg, storeArg, sdkVersionArg)
   if vccEnvStrTab != nil:
     for vccEnvKey, vccEnvVal in vccEnvStrTab:
       putEnv(vccEnvKey, vccEnvVal)