minor shader cache init fix

h3d/impl/ShaderCache.hx

@@ -4,8 +4,8 @@ class ShaderCache {
 
 	var file : String;
 	var outputFile : String;
-	var data : Map<String, haxe.io.Bytes> = null;
-	var sources : Map<String, String> = [];
+	var data : Map<String, haxe.io.Bytes>;
+	var sources : Map<String, String>;
 	var sourceFile : String;
 	public var keepSource : Bool;
 
@@ -18,6 +18,11 @@ class ShaderCache {
 	public function disableSave() {
 		outputFile = null;
 	}
+	
+	public function initEmpty() {
+		data = [];
+		sources = [];
+	}
 
 	function load() {
 		data = new Map();

hxsl/CacheFileBuilder.hx

@@ -234,6 +234,7 @@ class CacheFileBuilder {
 				builder.platforms.push(NXBinaries);
 			case "-build-cache":
 				builder.shaderCache = new h3d.impl.ShaderCache(getArg());
+				builder.shaderCache.initEmpty();
 			case "-build-cache-source":
 				builder.shaderCache.keepSource = true;
 			case "-build-cache-config":