Make null values loop-able.

hs-lsong · hs-lsong · commit 12f3d6069c76 · 2023-12-22T17:10:49.000-05:00
diff --git a/src/main/java/com/hubspot/jinjava/interpret/NullValue.java b/src/main/java/com/hubspot/jinjava/interpret/NullValue.java
@@ -0,0 +1,19 @@
+package com.hubspot.jinjava.interpret;
+
+/**
+ * Marker object of a `null` value. A null value in the map is usually considered
+ * the key does not exist. For example map = {"a": null}, if map.get("a") == null,
+ * we treat it as the there is not key "a" in the map.
+ */
+public final class NullValue {
+  public static final NullValue INSTANCE = new NullValue();
+
+  static NullValue instance() {
+    return INSTANCE;
+  }
+
+  @Override
+  public String toString() {
+    return "null";
+  }
+}
diff --git a/src/main/java/com/hubspot/jinjava/lib/tag/ForTag.java b/src/main/java/com/hubspot/jinjava/lib/tag/ForTag.java
@@ -27,6 +27,7 @@
 import com.hubspot.jinjava.interpret.InterpretException;
 import com.hubspot.jinjava.interpret.JinjavaInterpreter;
 import com.hubspot.jinjava.interpret.JinjavaInterpreter.InterpreterScopeClosable;
+import com.hubspot.jinjava.interpret.NullValue;
 import com.hubspot.jinjava.interpret.OutputTooBigException;
 import com.hubspot.jinjava.interpret.TemplateError;
 import com.hubspot.jinjava.interpret.TemplateSyntaxException;
@@ -200,7 +201,11 @@ public String renderForCollection(
 
         // set item variables
         if (loopVars.size() == 1) {
-          interpreter.getContext().put(loopVars.get(0), val);
+          if (val == null && interpreter.getContext().get(loopVars.get(0)) != null) {
+            interpreter.getContext().put(loopVars.get(0), NullValue.INSTANCE);
+          } else {
+            interpreter.getContext().put(loopVars.get(0), val);
+          }
         } else {
           for (int loopVarIndex = 0; loopVarIndex < loopVars.size(); loopVarIndex++) {
             String loopVar = loopVars.get(loopVarIndex);
diff --git a/src/test/java/com/hubspot/jinjava/lib/tag/ForTagTest.java b/src/test/java/com/hubspot/jinjava/lib/tag/ForTagTest.java
@@ -377,6 +377,18 @@ public void itAllowsCheckingOfWithinForLoop() throws NoSuchMethodException {
     assertThat(rendered.getOutput()).isEqualTo("false true true false");
   }
 
+  @Test
+  public void forLoopWithNullValues() {
+    context.put("number", -1);
+    context.put("the_list", Lists.newArrayList(1L, 2L, null, null, null));
+    TagNode tagNode = (TagNode) fixture("loop-last-var");
+    Document dom = Jsoup.parseBodyFragment(tag.interpret(tagNode, interpreter));
+
+    assertThat(dom.select("h3")).hasSize(4);
+    dom.outputSettings().prettyPrint(true).indentAmount(4);
+    assertThat(dom.html()).contains("seven: null");
+  }
+
   public static boolean inForLoop() {
     JinjavaInterpreter interpreter = JinjavaInterpreter.getCurrent();
     return interpreter.getContext().isInForLoop();
