Example of getting tripped up on bindings that are never used

ExampleMain.java

import com.google.inject.Binder;
import com.google.inject.Guice;
import com.google.inject.Inject;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Module;
import com.google.inject.TypeLiteral;
import com.google.inject.multibindings.MapBinder;
import com.google.inject.name.Names;

import java.util.Map;

/**
 */
public class ExampleMain
{
  public static void main(String[] args)
  {
    final Injector histInj = Guice.createInjector(new HistoricalModule(), new ExtensionModule());

    System.out.println("===========");
    outputMap(histInj.getInstance(Key.get(new TypeLiteral<Map<String, Extension>>(){}, Names.named("Historical"))));
    outputMap(histInj.getInstance(Key.get(new TypeLiteral<Map<String, Extension>>(){}, Names.named("Broker"))));
    System.out.println("||||||||||||");
    System.out.println();

    final Injector brokInj = Guice.createInjector(new BrokerModule(), new ExtensionModule());

    System.out.println("============");
    outputMap(brokInj.getInstance(Key.get(new TypeLiteral<Map<String, Extension>>(){}, Names.named("Broker"))));
    System.out.println("||||||||||||");
    System.out.println();
  }

  private static void outputMap(Map<String, Extension> extensions)
  {
    for (Map.Entry<String, Extension> entry : extensions.entrySet()) {
      System.out.printf("%8s => %s%n", entry.getKey(), entry.getValue().go());
    }
  }

  public static class HistoricalModule implements Module
  {
    @Override
    public void configure(Binder binder)
    {
      binder.bind(CharSequence.class).toInstance("WHOZI");
      binder.bind(String.class).toInstance("HOWDY");
    }
  }

  public static class BrokerModule implements Module
  {
    @Override
    public void configure(Binder binder)
    {
      binder.bind(String.class).toInstance("HOWDY");
    }
  }

  public static class ExtensionModule implements Module
  {
    @Override
    public void configure(Binder binder)
    {
      MapBinder.newMapBinder(binder, String.class, Extension.class, Names.named("Broker"))
               .addBinding("howdy")
               .to(BrokerExtension.class);

      MapBinder.newMapBinder(binder, String.class, Extension.class, Names.named("Historical"))
               .addBinding("3")
               .to(HistoricalExtension.class);
    }
  }

  public static interface Extension
  {
    public String go();
  }

  public static class BrokerExtension implements Extension
  {
    private final String msg;

    @Inject
    public BrokerExtension(
        String msg
    )
    {
      this.msg = msg;
    }

    @Override
    public String go()
    {
      return msg;
    }
  }

  public static class HistoricalExtension implements Extension
  {
    private final CharSequence val;

    @Inject
    public HistoricalExtension(
        CharSequence val
    )
    {
      this.val = val;
    }

    @Override
    public String go()
    {
      return val.toString();
    }
  }
}

output.txt

===========
       3 => WHOZI
   howdy => HOWDY
||||||||||||

Exception in thread "main" com.google.inject.CreationException: Guice creation errors:

1) No implementation for java.lang.CharSequence was bound.
  while locating java.lang.CharSequence
    for parameter 0 at io.druid.curator.discovery.ExampleMain$HistoricalExtension.<init>(ExampleMain.java:110)
  at io.druid.curator.discovery.ExampleMain$ExtensionModule.configure(ExampleMain.java:72)

1 error
  at com.google.inject.internal.Errors.throwCreationExceptionIfErrorsExist(Errors.java:448)
	at com.google.inject.internal.InternalInjectorCreator.initializeStatically(InternalInjectorCreator.java:155)
	at com.google.inject.internal.InternalInjectorCreator.build(InternalInjectorCreator.java:107)
	at com.google.inject.Guice.createInjector(Guice.java:96)
	at com.google.inject.Guice.createInjector(Guice.java:73)
	at com.google.inject.Guice.createInjector(Guice.java:62)
	at io.druid.curator.discovery.ExampleMain.main(ExampleMain.java:29)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at com.intellij.rt.execution.application.AppMain.main(AppMain.java:120)

Process finished with exit code 1