Attempt to invoke interface method 'java.lang.Object kotlin.Lazy.getValue()' on a null object reference

I'm not a pro but I'd like to tell you what I've found. Let's create a simple class to see how delegates in Kotlin work. Just in case, I'm using Kotlin 1.3.70. Here is our simple class:

class Test {
    val test by lazy { "test" }
}

In the Idea or Android Studio, you can check the bytecode. But it's pretty hard to read JVM bytecode at least for me :) Let's convert it to something looks like Java:

...
public final class Test {
   @NotNull
   private final Lazy test$delegate;

   @NotNull
   public final String getTest() {
      Lazy var1 = this.test$delegate;
      Object var3 = null;
      boolean var4 = false;
      return (String)var1.getValue();
   }

   public Test() {
      this.test$delegate = LazyKt.lazy((Function0)null.INSTANCE);
   }
}
...

As you see Kotlin creates a special field for lazy delegate which initializes in the constructor. The problem is Gson uses UnsafeAllocator and doesn't call the constructor. You can read a bit more about it for example here. So when you deserialize your Article object it contains null instead of appropriate lazy delegate. That's why you got a null pointer exception when trying to call this del