import com.intellij.util.io.VoidDataExternalizer; //导入依赖的package包/类
public VcsLogUserIndex(@Nonnull String logId,
                       @Nonnull VcsUserRegistryImpl userRegistry,
                       @Nonnull FatalErrorHandler consumer,
                       @Nonnull Disposable disposableParent) throws IOException {
  super(logId, USERS, getVersion(), new UserIndexer(userRegistry), VoidDataExternalizer.INSTANCE,
        consumer, disposableParent);
  myUserRegistry = userRegistry;
  ((UserIndexer)myIndexer).setFatalErrorConsumer(e -> consumer.consume(this, e));
}
 

import com.intellij.util.io.VoidDataExternalizer; //导入依赖的package包/类
@NotNull
@Override
public DataExternalizer<Void> getValueExternalizer() {
    return VoidDataExternalizer.INSTANCE;
}
 

import com.intellij.util.io.VoidDataExternalizer; //导入依赖的package包/类
@NotNull
public DataExternalizer<Void> getValueExternalizer() {
    return VoidDataExternalizer.INSTANCE;
}
 

import com.intellij.util.io.VoidDataExternalizer; //导入依赖的package包/类
@Nonnull
@Override
public final DataExternalizer<Void> getValueExternalizer() {
  return VoidDataExternalizer.INSTANCE;
}
 

import com.intellij.util.io.VoidDataExternalizer; //导入依赖的package包/类
public VcsLogMessagesTrigramIndex(@Nonnull String logId,
                                  @Nonnull FatalErrorHandler fatalErrorHandler,
                                  @Nonnull Disposable disposableParent) throws IOException {
  super(logId, TRIGRAMS, getVersion(), new TrigramMessageIndexer(), VoidDataExternalizer.INSTANCE,
        fatalErrorHandler, disposableParent);
}