[DO NOT MERGE] Test for google/gson#2729

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

@@ -0,0 +1,32 @@
+package com.google.gson;
+
+import com.google.gson.stream.JsonReader;
+import com.google.gson.stream.JsonWriter;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public final class TypeAdapterTest {
+
+	@Test
+	public void testTypeAdapterNullSafe() {
+		final TypeAdapter<?> unit = typeAdapter;
+		final TypeAdapter<?> nullSafeUnit1 = unit.nullSafe();
+		final TypeAdapter<?> nullSafeUnit2 = unit.nullSafe();
+		Assertions.assertNotSame(nullSafeUnit1, nullSafeUnit2);
+		Assertions.assertSame(nullSafeUnit1, nullSafeUnit2.nullSafe(), () -> String.format("Must pass the test once %s is resolved", "https://github.com/google/gson/issues/2729"));
+		Assertions.assertSame(nullSafeUnit1.nullSafe(), nullSafeUnit2, () -> String.format("Must pass the test once %s is resolved", "https://github.com/google/gson/issues/2729"));
+	}
+
+	private static final TypeAdapter<Object> typeAdapter = new TypeAdapter<>() {
+		@Override
+		public void write(final JsonWriter out, final Object value) {
+			throw new AssertionError();
+		}
+
+		@Override
+		public Object read(final JsonReader in) {
+			throw new AssertionError();
+		}
+	};
+
+}

src/test/java/com/google/gson/package-info.java

@@ -0,0 +1,4 @@
+@Nonnull
+package com.google.gson;
+
+import javax.annotation.Nonnull;