Require non null remote for auto-gen'd Java Proxy constructor.

It should fail early at the contructor, not at function calls.

Test: hidl_test_java

Change-Id: I7ad9bb3bf155bc7fe14c0b8f62332e70141bdbfd
diff --git a/generateJava.cpp b/generateJava.cpp
index e944431..a4b53b4 100644
--- a/generateJava.cpp
+++ b/generateJava.cpp
@@ -273,7 +273,7 @@
     out << "private android.os.IHwBinder mRemote;\n\n";
     out << "public Proxy(android.os.IHwBinder remote) {\n";
     out.indent();
-    out << "mRemote = remote;\n";
+    out << "mRemote = java.util.Objects.requireNonNull(remote);\n";
     out.unindent();
     out << "}\n\n";