Fix #5401 Single-arg method invocations should not fall back to input…

src/main/java/tools/jackson/databind/introspect/AnnotatedMethod.java

@@ -107,8 +107,7 @@ public final Object call(Object[] args) throws Exception {
     @Override
     public final Object call1(Object arg) throws Exception {
         try {
-            Object ret = _invokerUnary.get().invokeExact(arg);
-            return ret == null ? arg : ret;
+            return _invokerUnary.get().invokeExact(arg);
         } catch (final Throwable e) {
             throw sneakyThrow(e);
         }

src/test/java/tools/jackson/databind/deser/creators/JsonCreatorReturningNull4938Test.java

@@ -13,9 +13,11 @@
 import static org.junit.jupiter.api.Assertions.*;
 
 // [databind#4938] Allow JsonCreator factory method to return `null`
+// [databind#5401] Do not replace null from JsonCreator factory method
 public class JsonCreatorReturningNull4938Test
     extends DatabindTestUtil
 {
+    // [databind#4938]
     static class Localized3 {
         public final String en;
         public final String de;
@@ -89,12 +91,32 @@ public void addProperty(String key, Object value) {
         }
     }
 
+    // [databind#5401]
+    static class NonEmpty5401 {
+        public NonEmptyString5401 nonEmpty;
+    }
+
+    static class NonEmptyString5401 {
+        public final String value;
+
+        @JsonCreator
+        public static NonEmptyString5401 of(String value) {
+            if (value == null || value.isEmpty()) {
+                return null;
+            }
+            return new NonEmptyString5401(value);
+        }
+
+        private NonEmptyString5401(String value) {
+            this.value = value;
+        }
+    }
 
     private final ObjectMapper MAPPER = newJsonMapper();
 
+    // [databind#4938]
     @Test
     void testDeserializeToNullWhenAllPropertiesAreNull()
-            throws Exception
     {
         Localized3 result = MAPPER.readValue(
                 "{ \"en\": null, \"de\": null, \"fr\": null }",
@@ -105,7 +127,6 @@ void testDeserializeToNullWhenAllPropertiesAreNull()
 
     @Test
     void testDeserializeToNonNullWhenAnyPropertyIsNonNull()
-            throws Exception
     {
         Localized3 result = MAPPER.readValue(
                 "{ \"en\": \"Hello\", \"de\": null, \"fr\": null }",
@@ -117,7 +138,6 @@ void testDeserializeToNonNullWhenAnyPropertyIsNonNull()
 
     @Test
     void testDeserializeReadingAfterCreatorProps()
-            throws Exception
     {
         // Should all fail...
         ObjectReader enabled = MAPPER.readerFor(Localized4.class)
@@ -135,7 +155,6 @@ void testDeserializeReadingAfterCreatorProps()
     // Test to verify we are reading till the end of the OBJECT
     @Test
     void testDeserializeReadingUntilEndObject()
-            throws Exception
     {
         // Should all fail...
         ObjectReader enabled = MAPPER.readerFor(Localized4.class)
@@ -156,7 +175,6 @@ void testDeserializeReadingUntilEndObject()
 
     @Test
     void testJsonCreatorNullWithAnySetter()
-            throws Exception
     {
         String JSON = "{ \"en\": null, \"de\": null, \"fr\": null, " +
                 // These two properties are unknown
@@ -166,4 +184,16 @@ void testJsonCreatorNullWithAnySetter()
                 .without(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES)
                 .readValue(JSON);
     }
+
+    // [databind#5401]
+    @Test
+    void deserializeFieldToNullIfDelegatingCreatorReturnsNull()
+    {
+        NonEmpty5401 result = MAPPER.readValue(
+                "{ \"nonEmpty\": \"\" }",
+                NonEmpty5401.class);
+
+        assertNotNull(result);
+        assertNull(result.nonEmpty);
+    }
 }