Fix #2015 (or, rather, add test to verify, likely fixed with #2023)

Author: cowtowncoder

release-notes/VERSION-2.x

@@ -21,6 +21,9 @@ Project: jackson-databind
 #2001: Deserialization issue with `@JsonIgnore` and `@JsonCreator` + `@JsonProperty`
   for same property name
  (reported, fix contributed by Jakub S)
+#2015: `@Jsonsetter with Nulls.SKIP` collides with
+  `DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL` when parsing enum
+ (reported by ndori@github)
 #2016: Delegating JsonCreator disregards JsonDeserialize info
  (reported by Carter K)
 #2019: Abstract Type mapping in 2.9 fails when multiple modules are registered

src/test/java/com/fasterxml/jackson/databind/deser/filter/NullConversionsSkipTest.java

@@ -36,6 +36,16 @@ public void setValue(String v) {
         }
     }
 
+    // for [databind#2015]
+    enum NUMS2015 {
+        ONE, TWO
+    }
+
+    public static class Pojo2015 {
+        @JsonSetter(value = "number", nulls = Nulls.SKIP)
+        NUMS2015 number = NUMS2015.TWO;
+    }
+
     /*
     /**********************************************************
     /* Test methods, straight annotation
@@ -72,6 +82,15 @@ public void testSkipNullMethod() throws Exception
         assertEquals("a", result._nullsOk);
     }
 
+    // for [databind#2015]
+    public void testEnumAsNullThenSkip() throws Exception
+    {    
+        Pojo2015 p = MAPPER.readerFor(Pojo2015.class)
+                .with(DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_AS_NULL)
+                .readValue("{\"number\":\"THREE\"}"); 
+        assertEquals(NUMS2015.TWO, p.number);
+    }
+
     /*
     /**********************************************************
     /* Test methods, defaulting