[BUG] Compile fails f @SuperBuilder(toBuilder = true) with @Singular on a Map

[nadernader99]

Describe the bug

Compile fails when using a combination of @SuperBuilder(toBuilder = true) with @Singular on a Map field with error message 'no instance(s) of type variable(s) T exist so that java.util.List conforms to java.util.Map'

To Reproduce

Java source code:

import java.util.Map;

import lombok.Getter;
import lombok.Singular;
import lombok.experimental.SuperBuilder;

@SuperBuilder(toBuilder = true)
@Getter
public class SuperToBuilder {

    @Singular("addToMap")
    private final Map<String, String> itemMap;
}

Compile output:

$ javac -cp lombok-1.18.6.jar src/SuperToBuilder.java
src\SuperToBuilder.java:7: error: incompatible types: bad type in conditional expression
@SuperBuilder(toBuilder = true)
^
    no instance(s) of type variable(s) T exist so that List<T> conforms to Map<? extends String,? extends String>
  where T is a type-variable:
    T extends Object declared in method <T>emptyList()
Note: Some messages have been simplified; recompile with -Xdiags:verbose to get full output
1 error

--

Delombok shows the bug may be a simple
SuperToBuilderDelombok.java.gz
mismatch of logic for handling empty collections. A zip of the full delombok code has been attached to this issue.

        private static void $fillValuesFromInstanceIntoBuilder(final SuperToBuilderDelombok instance, final SuperToBuilderBuilder<?, ?> b) {
            b.itemMap(instance.itemMap == null ? java.util.Collections.emptyList() : instance.itemMap);
        }

Appearantly, java.util.Collections.emptyMap() should be selected in the case of a null Map.

This issue only occurs with the Combination of @SuperBuilder(toBuilder = true) and @Singular on a Map field. The following changes to the example all compiled sucessfully:

• @builder(toBuilder = true) instead of @SuperBuilder(toBuilder = true)
• @SuperBuilder() instead of @SuperBuilder(toBuilder = true)
• Remove @Singular from the Map
• Change the Map to a List or Set.

SuperToBuilderDelombok.java.gz

Expected behavior

The class should compile successfully and generate a builder with singular set methods for the Map.

Version info (please complete the following information):

Lombok Version: 1.18.6
Java Platform: OpenJDK 11.0.2 2019-01-15
OpenJDK Runtime Environment 18.9 (build 11.0.2+9) OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

Additional context

Attempted to use the latest edge-SNAPSHOT from https://projectlombok.org/edge-releases as of April 20, 2018, but the results were the same.

[janrieke]

Thanks for the detailed report. The issue is probably caused by the hard-coded List in HandleSuperBuilder:728.

[nadernader99]

I missed that this made it into 1.18.8 because I had worked around this issue. I've upgraded and verified that this problem issue fixed in my project. Thanks!