Assert for non-empty nulls

java/pom.xml

@@ -153,6 +153,7 @@
     </dependencies>
 
     <properties>
+        <argLine>-da:ai.rapids.cudf.AssertEmptyNulls</argLine>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven.compiler.source>1.8</maven.compiler.source>
         <maven.compiler.target>1.8</maven.compiler.target>

java/src/main/java/ai/rapids/cudf/AssertEmptyNulls.java

@@ -0,0 +1,43 @@
+/*
+ *
+ *  Copyright (c) 2023, NVIDIA CORPORATION.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ *
+ */
+
+package ai.rapids.cudf;
+
+/**
+ *  This class is a Helper class to assert there are no non-empty nulls in a ColumnView
+ *
+ *  The reason for the existence of this class is so that we can turn the asserts on/off when needed
+ *  by passing "-da:ai.rapids.cudf.AssertEmptyNulls". We need that behavior because we have tests
+ *  that explicitly test with ColumnViews that contain non-empty nulls but more importantly, there
+ *  could be cases where an external system may not have a requirement of nulls being empty, so for
+ *  us to work with those systems, we can turn off this assert in the field.
+ */
+public class AssertEmptyNulls {
+  // This is the recommended way to check at runtime that assertions are enabled.
+  // https://docs.oracle.com/javase/8/docs/technotes/guides/language/assert.html
+  private static boolean assertNullsAreEmpty = false;
+  static {
+      assert assertNullsAreEmpty = true ; // Intentional side effect
+  }
+
+  public static void assertNullsAreEmpty(ColumnView cv) {
+    if (cv.type.isNestedType() || cv.type.hasOffsets() && assertNullsAreEmpty) {
+      assert !cv.hasNonEmptyNulls() : "Column has non-empty nulls";
+    }
+  }
+}

java/src/main/java/ai/rapids/cudf/ColumnView.java

@@ -52,6 +52,7 @@ public class ColumnView implements AutoCloseable, BinaryOperable {
     this.rows = ColumnView.getNativeRowCount(viewHandle);
     this.nullCount = ColumnView.getNativeNullCount(viewHandle);
     this.offHeap = null;
+    AssertEmptyNulls.assertNullsAreEmpty(this);
   }
 
 
@@ -67,6 +68,7 @@ protected ColumnView(ColumnVector.OffHeapState state) {
     type = DType.fromNative(ColumnView.getNativeTypeId(viewHandle), ColumnView.getNativeTypeScale(viewHandle));
     rows = ColumnView.getNativeRowCount(viewHandle);
     nullCount = ColumnView.getNativeNullCount(viewHandle);
+    AssertEmptyNulls.assertNullsAreEmpty(this);
   }
 
   /**