Add no-arg ctor to BaseGradientAdapter

Signed-off-by: Ryan Nett <[email protected]>

Author: rnett

tensorflow-core/tensorflow-core-api/src/main/java/org/tensorflow/BaseGradientAdapter.java

@@ -28,6 +28,10 @@
 /** Helper base class for custom gradient adapters <b>INTERNAL USE ONLY</b> */
 public abstract class BaseGradientAdapter extends GradFunc {
 
+  protected BaseGradientAdapter() {
+    super();
+  }
+
   /**
    * Convert an array of native outputs to a list of {@link Output}s.
    *