Formalize null handling of type tokens

gson/src/main/java/com/google/gson/Gson.java

@@ -111,7 +111,6 @@ public final class Gson {
   static final boolean DEFAULT_COMPLEX_MAP_KEYS = false;
   static final boolean DEFAULT_SPECIALIZE_FLOAT_VALUES = false;
 
-  private static final TypeToken<?> NULL_KEY_SURROGATE = TypeToken.get(Object.class);
   private static final String JSON_NON_EXECUTABLE_PREFIX = ")]}'\n";
 
   /**
@@ -440,7 +439,11 @@ private static TypeAdapter<AtomicLongArray> atomicLongArrayAdapter(final TypeAda
    */
   @SuppressWarnings("unchecked")
   public <T> TypeAdapter<T> getAdapter(TypeToken<T> type) {
-    TypeAdapter<?> cached = typeTokenCache.get(type == null ? NULL_KEY_SURROGATE : type);
+    if (type == null) {
+      throw new NullPointerException("No type specified");
+    }
+
+    TypeAdapter<?> cached = typeTokenCache.get(type);
     if (cached != null) {
       return (TypeAdapter<T>) cached;
     }

gson/src/test/java/com/google/gson/GsonTest.java

@@ -17,6 +17,7 @@
 package com.google.gson;
 
 import com.google.gson.internal.Excluder;
+import com.google.gson.reflect.TypeToken;
 import com.google.gson.stream.JsonReader;
 import com.google.gson.stream.JsonWriter;
 import java.io.IOException;
@@ -26,6 +27,9 @@
 import java.util.ArrayList;
 import java.util.HashMap;
 import junit.framework.TestCase;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.ExpectedException;
 
 /**
  * Unit tests for {@link Gson}.
@@ -82,4 +86,16 @@ private static final class TestTypeAdapter extends TypeAdapter<Object> {
     }
     @Override public Object read(JsonReader in) throws IOException { return null; }
   }
+
+  public void testNullAdapterLookup() {
+    // Formalize the handling of null type tokens (previously it was partially handled, but still throwing an error)
+    // Note: ExpectedException cannot be used due to test suite extending TestCase
+    try {
+      new Gson().getAdapter((TypeToken<Object>) null);
+      assertTrue("Unreachable", false);
+    }
+    catch (NullPointerException e) {
+      assertEquals("No type specified", e.getMessage());
+    }
+  }
 }