libhidladapter: handle nullptr interface

Bug: 37518178
Test: adapt ashmem hal and have YT get memory from it
Change-Id: I4cbecde14d4c175cd8acc21719fc5d08570896c4
diff --git a/adapter/HidlBinderAdapter.cpp b/adapter/HidlBinderAdapter.cpp
index e769cb5..4efe9fb 100644
--- a/adapter/HidlBinderAdapter.cpp
+++ b/adapter/HidlBinderAdapter.cpp
@@ -109,6 +109,10 @@
                            const std::function<sp<IBase>()>& makeDefault) {
     static std::map<sp<IBase>, sp<IBase>> sAdapterMap;
 
+    if (something == nullptr) {
+        return something;
+    }
+
     auto it = sAdapterMap.find(something);
     if (it == sAdapterMap.end()) {
         it = sAdapterMap.insert(it, {something, makeDefault()});