feat(msgpack-json-el): allow non-strict condtions

Allows JsonPath conditions to be non-strict, evaluating to null when no values were found

docs/src/reference/json-conditions.md

@@ -49,7 +49,33 @@ $.orderCount >= 5 && $.orderCount < 15
 </table>
 
 A Null-Value can be used to check if a property is set (e.g., `$.owner == null`).
-If the property doesn't exist, then the JSON Path evaluation fails.
+If the any property in specified JSON Path doesn't exist, then it would be resolved as `null` and could be compared as such.
+
+<table style="width:100%">
+  <tr>
+    <th>Payload</th>
+    <th>JSON Path</th>
+    <th>Value</th
+  </tr>
+
+  <tr>
+    <td>{"foo": 3}</td>
+    <td>$.foo</td>
+    <td>3</td>
+  </tr>
+
+  <tr>
+    <td>{"foo": 3}</td>
+    <td>$.bar</td>
+    <td>null</td>
+  </tr>
+
+  <tr>
+    <td>{"foo": 3}</td>
+    <td>$.bar.baz</td>
+    <td>null</td>
+  </tr>
+</table>
 
 ### Comparison Operators
 
@@ -100,6 +126,7 @@ If the property doesn't exist, then the JSON Path evaluation fails.
 The operators `<`, `<=`, `>` and `>=` can only be used for numbers.
 
 If the values of an operator have different types, then the evaluation fails.
+Comparing null or missing property with a number is considered as comparing different types.
 
 ### Logical Operators
 

json-el/src/main/java/io/zeebe/msgpack/el/JsonConditionInterpreter.java

@@ -37,12 +37,11 @@ public class JsonConditionInterpreter {
 
   public boolean eval(final JsonCondition condition, final DirectBuffer json) {
     cache.wrap(json);
-
     return evalCondition(condition, json);
   }
 
   private boolean evalCondition(final JsonCondition condition, final DirectBuffer json) {
-    boolean isFulFilled = false;
+    final boolean isFulFilled;
 
     if (condition instanceof Comparison) {
       isFulFilled = evalComparison((Comparison) condition, json);
@@ -105,9 +104,17 @@ private MsgPackToken getPathResult(
     final DirectBuffer resultBuffer = cachable ? cache.get(pathId) : null;
 
     if (resultBuffer != null) {
+      if (resultBuffer.capacity() == 0) {
+        return MsgPackToken.NIL;
+      }
       msgPackReader.wrap(resultBuffer, 0, resultBuffer.capacity());
     } else {
-      readQueryResult(path.query(), json);
+      if (!readQueryResult(path.query(), json)) {
+        if (cachable) {
+          cache.put(pathId, 0, 0);
+        }
+        return MsgPackToken.NIL;
+      }
 
       final int offset = visitor.currentResultPosition();
       final int length = visitor.currentResultLength();
@@ -122,15 +129,14 @@ private MsgPackToken getPathResult(
     return msgPackReader.readToken();
   }
 
-  private void readQueryResult(JsonPathQuery query, DirectBuffer json) {
+  private boolean readQueryResult(JsonPathQuery query, DirectBuffer json) {
     visitor.init(query.getFilters(), query.getFilterInstances());
     traverser.wrap(json, 0, json.capacity());
 
     traverser.traverse(visitor);
 
     if (visitor.numResults() == 0) {
-      throw new JsonConditionException(
-          String.format("JSON path '%s' has no result.", bufferAsString(query.getExpression())));
+      return false;
     } else if (visitor.numResults() > 1) {
       // such a JSON path expression should not be valid
       throw new JsonConditionException(
@@ -139,13 +145,12 @@ private void readQueryResult(JsonPathQuery query, DirectBuffer json) {
     }
 
     visitor.moveToResult(0);
+    return true;
   }
 
   private boolean equals(MsgPackToken x, MsgPackToken y) {
-    if (x.getType() == MsgPackType.NIL) {
-      return y.getType() == MsgPackType.NIL;
-    } else if (y.getType() == MsgPackType.NIL) {
-      return false;
+    if (x.getType() == MsgPackType.NIL || y.getType() == MsgPackType.NIL) {
+      return x.getType() == y.getType();
     } else {
       ensureSameType(x, y);
 

json-el/src/test/java/io/zeebe/msgpack/el/JsonConditionTest.java

@@ -78,16 +78,37 @@ public void shouldFailIfTypeDoesntMatch() {
   }
 
   @Test
-  public void shouldFailIfJsonPathDoesntMatch() {
+  public void shouldFailIfMissingPropertyComparedRelatively() {
     final CompiledJsonCondition condition = JsonConditionFactory.createCondition("$.foo > 3");
     assertThat(condition.isValid()).isTrue();
 
     thrown.expect(JsonConditionException.class);
-    thrown.expectMessage("JSON path '$.foo' has no result");
+    thrown.expectMessage("Cannot compare values of different types: NIL and INTEGER");
 
     interpreter.eval(condition.getCondition(), asMsgPack("bar", 4));
   }
 
+  @Test
+  public void shouldEqualToNullIfJsonPathDoesntMatch() {
+    final CompiledJsonCondition condition = JsonConditionFactory.createCondition("$.foo == null");
+    assertThat(condition.isValid()).isTrue();
+
+    final boolean result = interpreter.eval(condition.getCondition(), asMsgPack("bar", 4));
+
+    assertThat(result).isTrue();
+  }
+
+  @Test
+  public void shouldEqualToNullIfAnySegmentInJsonPathDoesntMatch() {
+    final CompiledJsonCondition condition =
+        JsonConditionFactory.createCondition("$.foo.baz == null");
+    assertThat(condition.isValid()).isTrue();
+
+    final boolean result = interpreter.eval(condition.getCondition(), asMsgPack("bar", 4));
+
+    assertThat(result).isTrue();
+  }
+
   @Test
   public void shouldFailIfTypeIsNil() {
     final CompiledJsonCondition condition = JsonConditionFactory.createCondition("$.foo > 3");

msgpack-core/src/main/java/io/zeebe/msgpack/spec/MsgPackToken.java

@@ -19,10 +19,11 @@
 import org.agrona.concurrent.UnsafeBuffer;
 
 public class MsgPackToken {
+  public static final MsgPackToken NIL = new MsgPackToken();
 
   protected static final int MAX_MAP_ELEMENTS = 0x3fff_ffff;
 
-  protected MsgPackType type;
+  protected MsgPackType type = MsgPackType.NIL;
   protected int totalLength;
 
   // string