Add IsNull expression to vortex-jni (#7358)

Add IsNull to vortex-jni bindings

---------

Signed-off-by: Robert Kruszewski <github@robertk.io>

Author: robert3005

java/testfiles/Cargo.lock

@@ -87,6 +87,14 @@ interface Visitor<T> {
          */
         T visitGetItem(GetItem getItem);
 
+        /**
+         * Visits an is null expression (null check).
+         *
+         * @param isNull the is null expression to visit
+         * @return the result of visiting the is null expression
+         */
+        T visitIsNull(IsNull isNull);
+
         /**
          * For expressions that do not have a specific visitor method.
          */

java/vortex-jni/src/main/java/dev/vortex/api/Expression.java

@@ -0,0 +1,99 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: Copyright the Vortex contributors
+
+package dev.vortex.api.expressions;
+
+import dev.vortex.api.Expression;
+import java.util.List;
+import java.util.Objects;
+import java.util.Optional;
+
+/**
+ * Represents an IS NULL expression that checks whether values are null.
+ * This expression returns true for null values and false for non-null values.
+ */
+public final class IsNull implements Expression {
+    private final Expression child;
+
+    private IsNull(Expression child) {
+        this.child = child;
+    }
+
+    /**
+     * Parses an IsNull expression from serialized metadata and child expressions.
+     * This method is used during deserialization of Vortex expressions.
+     *
+     * @param metadata the serialized metadata, must be empty for IsNull expressions
+     * @param children the child expressions, must contain exactly one element
+     * @return a new IsNull expression parsed from the provided data
+     * @throws IllegalArgumentException if the number of children is not exactly one,
+     *                                  or if metadata is not empty
+     */
+    public static IsNull parse(byte[] metadata, List<Expression> children) {
+        if (children.size() != 1) {
+            throw new IllegalArgumentException(
+                    "IsNull expression must have exactly one child, found: " + children.size());
+        }
+        if (metadata.length > 0) {
+            throw new IllegalArgumentException(
+                    "IsNull expression must not have metadata, found: " + metadata.length);
+        }
+        return new IsNull(children.get(0));
+    }
+
+    /**
+     * Creates a new IsNull expression that checks nullity of the given child expression.
+     *
+     * @param child the expression to check for null values
+     * @return a new IsNull expression
+     */
+    public static IsNull of(Expression child) {
+        return new IsNull(child);
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) return false;
+        IsNull other = (IsNull) o;
+        return Objects.equals(child, other.child);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(child);
+    }
+
+    @Override
+    public String id() {
+        return "vortex.is_null";
+    }
+
+    @Override
+    public List<Expression> children() {
+        return List.of(child);
+    }
+
+    @Override
+    public Optional<byte[]> metadata() {
+        return Optional.of(new byte[] {});
+    }
+
+    @Override
+    public String toString() {
+        return "vortex.is_null(" + child + ")";
+    }
+
+    /**
+     * Returns the child expression that will be checked for null values.
+     *
+     * @return the child expression
+     */
+    public Expression getChild() {
+        return child;
+    }
+
+    @Override
+    public <T> T accept(Visitor<T> visitor) {
+        return visitor.visitIsNull(this);
+    }
+}

java/vortex-jni/src/main/java/dev/vortex/api/expressions/IsNull.java

@@ -56,6 +56,8 @@ public static Expression deserialize(ExprProtos.Expr expr) {
                 return Literal.parse(metadata, children);
             case "vortex.not":
                 return Not.parse(metadata, children);
+            case "vortex.is_null":
+                return IsNull.parse(metadata, children);
             default:
                 return new Unknown(expr.getId(), children, expr.getMetadata().toByteArray());
         }

java/vortex-jni/src/main/java/dev/vortex/api/proto/Expressions.java

@@ -22,4 +22,12 @@ public void testRoundTrip() {
         Expression deserialized = Expressions.deserialize(proto);
         assertEquals(expression, deserialized);
     }
+
+    @Test
+    public void testIsNullRoundTrip() {
+        Expression expression = IsNull.of(GetItem.of(Root.INSTANCE, "a.b.c"));
+        ExprProtos.Expr proto = Expressions.serialize(expression);
+        Expression deserialized = Expressions.deserialize(proto);
+        assertEquals(expression, deserialized);
+    }
 }