Fix #3171

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -10,6 +10,8 @@ Project: jackson-databind
  (reported by JoeWoo; fix provided by drekbour@github)
 #3146: Merge findInjectableValues() results in AnnotationIntrospectorPair
  (contributed by Joe B)
+#3171: READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE doesn't work with empty strings
+ (reported by unintended@github)
 
 2.12.3 (12-Apr-2021)
 

src/main/java/com/fasterxml/jackson/databind/deser/std/EnumDeserializer.java

@@ -273,6 +273,16 @@ private final Object _deserializeAltString(JsonParser p, DeserializationContext
     {
         String name = nameOrig.trim();
         if (name.isEmpty()) { // empty or blank
+            // 07-Jun-2021, tatu: [databind#3171] Need to consider Default value first
+            //   (alas there's bit of duplication here)
+            if ((_enumDefaultValue != null)
+                    && ctxt.isEnabled(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE)) {
+                return _enumDefaultValue;
+            }
+            if (ctxt.isEnabled(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL)) {
+                return null;
+            }
+
             CoercionAction act;
             if (nameOrig.isEmpty()) {
                 act = _findCoercionFromEmptyString(ctxt);
@@ -323,11 +333,11 @@ private final Object _deserializeAltString(JsonParser p, DeserializationContext
                 && ctxt.isEnabled(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE)) {
             return _enumDefaultValue;
         }
-        if (!ctxt.isEnabled(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL)) {
-            return ctxt.handleWeirdStringValue(_enumClass(), name,
-                    "not one of the values accepted for Enum class: %s",  lookup.keys());
+        if (ctxt.isEnabled(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL)) {
+            return null;
         }
-        return null;
+        return ctxt.handleWeirdStringValue(_enumClass(), name,
+                "not one of the values accepted for Enum class: %s",  lookup.keys());
     }
 
     protected Object _deserializeOther(JsonParser p, DeserializationContext ctxt) throws IOException

src/test/java/com/fasterxml/jackson/databind/deser/jdk/EnumDefaultReadTest.java

@@ -218,6 +218,14 @@ public void testEmptyStringAsDefault() throws Exception
                 r.readValue(quote("Zero")));
         assertEquals(SimpleEnumWithDefault.ZERO,
                 r.readValue(quote("")));
+        assertEquals(SimpleEnumWithDefault.ZERO,
+                r.readValue(quote("    ")));
+
+        // Also check with `null` coercion as well
+        ObjectReader r2 = MAPPER.readerFor(SimpleEnumWithDefault.class)
+                .with(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL);
+        assertNull(r2.readValue(quote("")));
+        assertNull(r2.readValue(quote("    ")));
     }
 
     private <T> void _verifyOkDeserialization(ObjectReader reader, String fromValue,