Custom types on main parameters don't appear to work. (1.72)

My reduced test case is as follows:

public class Main {

    public static class CustomType {
        private String something;

        public CustomType(String something) {
            this.something = something;
        }
    }

    public static class CustomTypeConverter implements IStringConverter<CustomType> {
        @Override
        public CustomType convert(String value) {
            return new CustomType(value);
        }
    }
    
    @Parameters
    public static class ExampleCommandArgs {
        @Parameter(converter = CustomTypeConverter.class, required = true)
        public CustomType mainArg;

    }

    public static void main(String[] args) {
        JCommander.newBuilder()
                .addObject(new ExampleCommandArgs())
                .build()
                .parse(args);
    }
}

As far as I can see I’ve configured the converter properly, but the error I get is:

Exception in thread "main" com.beust.jcommander.ParameterException: Could not invoke null
    Reason: Can not set Main$CustomType field Main$ExampleCommandArgs.mainArg to java.lang.String
	at com.beust.jcommander.Parameterized.set(Parameterized.java:263)
	at com.beust.jcommander.JCommander$MainParameter.addValue(JCommander.java:101)
	at com.beust.jcommander.JCommander.parseValues(JCommander.java:773)
	at com.beust.jcommander.JCommander.parse(JCommander.java:340)
	at com.beust.jcommander.JCommander.parse(JCommander.java:319)
	at Main.main(Main.java:38)

Note I get the same error on main arguments on commands as well.

[RealSkeptic]

Hi. I was about to post this same bug.

To be exact, custom types cannot be used in a main parameter, unless the main parameter is a list.

Here is an example that exhibits this problem:

package testing;

import java.nio.file.Path;

import com.beust.jcommander.JCommander;
import com.beust.jcommander.Parameter;
import com.beust.jcommander.converters.PathConverter;

public class JcommanderTest {

    @Parameter( converter = PathConverter.class )
    public Path filepath;
    
    public static void main(String[] args) {
        JcommanderTest cmd = new JcommanderTest();
        String[] argv = { "/tmp/file.txt" };
        
        JCommander.newBuilder().addObject(cmd).build().parse(argv);
        
        System.out.printf("The filepath is %s class %s%n", cmd.filepath, cmd.filepath.getClass().getName());
        
    }
}

The result is:

Exception in thread "main" com.beust.jcommander.ParameterException: Could not invoke null
    Reason: Can not set java.nio.file.Path field testing.JcommanderTest.filepath to java.lang.String
	at com.beust.jcommander.Parameterized.set(Parameterized.java:273)
	at com.beust.jcommander.JCommander$MainParameter.addValue(JCommander.java:101)
	at com.beust.jcommander.JCommander.parseValues(JCommander.java:771)
	at com.beust.jcommander.JCommander.parse(JCommander.java:342)
	at com.beust.jcommander.JCommander.parse(JCommander.java:321)
	at testing.JcommanderTest.main(JcommanderTest.java:18)

If I add names, or if I declare the parameter as List<Path> instead of Path, this works properly.

[juewe]

Since this is a dupe of #380 and #380 is done with #390 one should close this?