Unknown token in filter is treated as 0 #382

src/main/java/com/hubspot/jinjava/lib/filter/AddFilter.java

@@ -74,7 +74,7 @@ public Object filter(Object object, JinjavaInterpreter interpreter, String... ar
     }
 
     if (args[0] == null) {
-      return base;
+      return null;
     }
 
     BigDecimal addend;

src/test/java/com/hubspot/jinjava/lib/filter/AddFilterTest.java

@@ -0,0 +1,32 @@
+package com.hubspot.jinjava.lib.filter;
+
+import com.google.common.collect.ImmutableMap;
+import com.hubspot.jinjava.BaseInterpretingTest;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.Map;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class AddFilterTest extends BaseInterpretingTest {
+    private Map<String, Object> bindings;
+
+    @Before
+    public void setup() {
+        jinjava.getGlobalContext().registerClasses(AddFilter.class);
+
+        bindings = ImmutableMap.of(
+                "num1", 12,
+                "num2", 48
+        );
+    }
+
+    @Test
+    public void itAddsNumber() {
+        assertThat(jinjava.render("{{ 5|add(13) }}", bindings)).isEqualTo("18");
+        assertThat(jinjava.render("{{ num1|add(4) }}", bindings)).isEqualTo("16");
+        assertThat(jinjava.render("{{ 7|add(num2) }}", bindings)).isEqualTo("55");
+        assertThat(jinjava.render("{{ num1|add(num2) }}", bindings)).isEqualTo("60");
+    }
+}