support null data in nodes (#4380)

src/main/java/com/fasterxml/jackson/databind/node/BigIntegerNode.java

@@ -3,6 +3,7 @@
 import java.io.IOException;
 import java.math.BigDecimal;
 import java.math.BigInteger;
+import java.util.Objects;
 
 import com.fasterxml.jackson.core.*;
 import com.fasterxml.jackson.databind.SerializerProvider;
@@ -113,11 +114,12 @@ public boolean equals(Object o)
         if (!(o instanceof BigIntegerNode)) {
             return false;
         }
-        return ((BigIntegerNode) o)._value.equals(_value);
+        BigIntegerNode otherNode = (BigIntegerNode) o;
+        return Objects.equals(otherNode._value, _value);
     }
 
     @Override
     public int hashCode() {
-        return _value.hashCode();
+        return Objects.hashCode(_value);
     }
 }

src/main/java/com/fasterxml/jackson/databind/node/DecimalNode.java

@@ -126,11 +126,23 @@ public boolean equals(Object o)
         if (o == this) return true;
         if (o == null) return false;
         if (o instanceof DecimalNode) {
-            return ((DecimalNode) o)._value.compareTo(_value) == 0;
+            DecimalNode otherNode = (DecimalNode) o;
+            if (otherNode._value == null) {
+                return _value == null;
+            } else if (_value == null) {
+                return false;
+            }
+            return otherNode._value.compareTo(_value) == 0;
         }
         return false;
     }
 
     @Override
-    public int hashCode() { return Double.valueOf(doubleValue()).hashCode(); }
+    public int hashCode() {
+        if (_value == null) {
+            // we need a stable hash code for _value == null
+            return 0;
+        }
+        return Double.valueOf(doubleValue()).hashCode();
+    }
 }

src/test/java/com/fasterxml/jackson/databind/node/NullDataEqualsTest.java

@@ -0,0 +1,35 @@
+package com.fasterxml.jackson.databind.node;
+
+import org.junit.jupiter.api.Test;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotEquals;
+
+public class NullDataEqualsTest {
+    @Test
+    void testNullBinaryNode() {
+        assertEquals(new BinaryNode(null), new BinaryNode(null));
+        assertNotEquals(new BinaryNode(new byte[8]), new BinaryNode(null));
+        assertNotEquals(new BinaryNode(null), new BinaryNode(new byte[8]));
+        assertEquals(-1, new BinaryNode(null).hashCode());
+    }
+
+    @Test
+    void testNullBigIntegerNode() {
+        assertEquals(new BigIntegerNode(null), new BigIntegerNode(null));
+        assertNotEquals(new BigIntegerNode(BigInteger.ZERO), new BigIntegerNode(null));
+        assertNotEquals(new BigIntegerNode(null), new BigIntegerNode(BigInteger.ZERO));
+        assertEquals(0, new BigIntegerNode(null).hashCode());
+    }
+
+    @Test
+    void testNullDecimalNode() {
+        assertEquals(new DecimalNode(null), new DecimalNode(null));
+        assertNotEquals(new DecimalNode(BigDecimal.ZERO), new DecimalNode(null));
+        assertNotEquals( new DecimalNode(null), new DecimalNode(BigDecimal.ZERO));
+        assertEquals(0, new DecimalNode(null).hashCode());
+    }
+}