# devopsgym / codegen__fasterxml__jackson-databind-4360

- taskset: [devopsgym](https://harnessreport.com/tasks/devopsgym.md)
- difficulty: hard
- category: code-generation
- language: 
- runnable from the site: no
- agent timeout: 3000s

## Results by harness

_none yet_

## Instruction

```
This is a code generation task. You are expected to write working code that solves the described problem.
<issue>
      ### Search before asking

- [X] I searched in the [issues](https://github.com/FasterXML/jackson-databind/issues) and found nothing similar.

### Describe the bug

After upgrading to 2.16.1, I cannot obtain `ObjectWriter` for enum classes, which some of the value returns `null` from `toString()`.

This used to work in 2.15.3

### Version Information

2.16.0, 2.16.1

### Reproduction

Following is the minimum JUnit 5 reproducer.

This works fine on 2.15.3 but exceptionally fails at `assertDoesNotThrow(..)` on 2.16.0 or 2.16.1. 


```java
    enum NullToStringEnum {
        ALPHA("A"),
        BETA("B"),
        UNDEFINED(null);

        private final String s;

        NullToStringEnum(String s) {
            this.s = s;
        }

        @Override
        public String toString() {
            return s;
        }
    }

    @Test
    void nullToStringEnum() {
        ObjectMapper mapper = new ObjectMapper();
        assertDoesNotThrow(() -> mapper.writerFor(NullToStringEnum.class));
        assertEquals("\"ALPHA\"", w.writeValueAsString(NullToStringEnum.ALPHA));
        assertEquals("\"UNDEFINED\"", w.writeValueAsString(NullToStringEnum.UNDEFINED));
    }
```

backtrace looks like:
```
Caused by: java.lang.IllegalStateException: Null String illegal for SerializedString
    at com.fasterxml.jackson.core.io.SerializedString.<init>(SerializedString.java:53)
    at com.fasterxml.jackson.databind.cfg.MapperConfig.compileString(MapperConfig.java:245)
    at com.fasterxml.jackson.databind.util.EnumValues.constructFromToString(EnumValues.java:136)
    at com.fasterxml.jackson.databind.ser.std.EnumSerializer.construct(EnumSerializer.java:125)
    at com.fasterxml.jackson.databind.ser.BasicSerializerFactory.buildEnumSerializer(BasicSerializerFactory.java:1218)
    at com.fasterxml.jackson.databind.ser.BasicSerializerFactory.findSerializerByPrimaryType(BasicSerializerFactory.java:428)
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory._createSerializer2(BeanSerializerFactory.java:235)
    at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.createSerializer(BeanSerializerFactory.java:174)
    at com.fasterxml.jackson.databind.SerializerProvider._createUntypedSerializer(SerializerProvider.java:1525)
    at com.fasterxml.jackson.databind.SerializerProvider._createAndCacheUntypedSerializer(SerializerProvider.java:1493)
    at com.fasterxml.jackson.databind.SerializerProvider.findValueSerializer(SerializerProvider.java:619)
    at com.fasterxml.jackson.databind.SerializerProvider.findTypedValueSerializer(SerializerProvider.java:901)
    at com.fasterxml.jackson.databind.ObjectWriter$Prefetch.forRootType(ObjectWriter.java:1535)
    at com.fasterxml.jackson.databind.ObjectWriter.<init>(ObjectWriter.java:116)
    at com.fasterxml.jackson.databind.ObjectMapper._newWriter(ObjectMapper.java:838)
    at com.fasterxml.jackson.databind.ObjectMapper.writerFor(ObjectMapper.java:4135)
    at org.example.MainTest.lambda$nullToStringEnum$0(MainTest.java:31)
    at org.junit.jupiter.api.AssertDoesNotThrow.assertDoesNotThrow(AssertDoesNotThrow.java:71)
```


### Expected behavior

Be able to serialize Enums even though it's `#toString()` returns `null`

### Additional context

Returning `null` from `toString()` is probably bad practice, but such Enums are out there in the wild.


From the 2.16.1 backtrace, it seems to be related to the change #4039

Building `EnumValues valuesByToString` regardless of the `SerializationFeature.WRITE_ENUMS_USING_TO_STRING` config might be the issue?

</issue>
Focus on implementing the required functionality correctly and efficiently. Treat this as a programming challenge.
You are not allowed to read git history.
```
---
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