Fix #4896: deserialize enum from ""

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/databind/util/CompactStringObjectMap.java

@@ -96,7 +96,8 @@ private final static int findSize(int size)
         return result;
     }
 
-    public Object find(String key) {
+    public Object find(String key)
+    {
         int slot = key.hashCode() & _hashMask;
         int ix = (slot<<1);
         Object match = _hashArea[ix];

src/test/java/com/fasterxml/jackson/databind/deser/enums/EnumDeserializationTest.java

@@ -206,7 +206,6 @@ public Object deserializeKey(String key, DeserializationContext ctxt) throws IOE
         }
     }
 
-
     @JsonDeserialize(using = AnEnumDeserializer.class, keyUsing = AnEnumKeyDeserializer.class)
     public enum LanguageCodeMixin {
     }
@@ -280,6 +279,18 @@ public static Operation3006 forValue(final String idStr) {
         }
     }
 
+    // [databind#4896]
+    enum YesOrNoOrEmpty4896 {
+        @JsonProperty("")
+        EMPTY,
+
+        @JsonProperty("yes")
+        YES,
+
+        @JsonProperty("no")
+        NO;
+    }
+
     /*
     /**********************************************************
     /* Test methods
@@ -810,4 +821,15 @@ public void testEnumFeature_READ_ENUM_KEYS_USING_INDEX_isDisabledByDefault() {
             .isEnabled(EnumFeature.READ_ENUM_KEYS_USING_INDEX));
     }
 
+    // [databind#4896]
+    @Test
+    public void testEnumReadFromEmptyString() throws Exception {
+        // First, regular value
+        assertEquals(YesOrNoOrEmpty4896.YES,
+                MAPPER.readerFor(YesOrNoOrEmpty4896.class)
+                    .readValue(q("yes")));
+        assertEquals(YesOrNoOrEmpty4896.EMPTY,
+            MAPPER.readerFor(YesOrNoOrEmpty4896.class)
+                .readValue(q("")));
+    }
 }