code: protected ManagedIndexBuilder getIndexBuilder( IndexDefinition defn, 
                                                     String workspaceName,
                                                     NodeTypes.Supplier nodeTypesSupplier, 
                                                     NodeTypePredicate matcher ) {
          // this returns null for backwards compatibility reasons (otherwise it should've been abstract)
          return null;
      }
docs: Offers subclasses the possibility of providing a {@link ManagedIndexBuilder} instance which significantly simplifies the
  task of creating or updating {@link ManagedIndex} instances for providers.
  <p>
  If a provider chooses to override this method, it does not have to override
  the {@link #createIndex(IndexDefinition, String, NodeTypes.Supplier, NodeTypePredicate, IndexFeedback)} method or
  the {@link #updateIndex(IndexDefinition, IndexDefinition, ManagedIndex, String, NodeTypes.Supplier, NodeTypePredicate, IndexFeedback)}
  method, as the builder instance will be used to create specific indexes and adapters, based on the index definition.
  </p>
  <p>
  Providers can also choose to ignore this method, in which case they will have to override the
  {@link #createIndex(IndexDefinition, String, NodeTypes.Supplier, NodeTypePredicate, IndexFeedback)} and
  {@link #updateIndex(IndexDefinition, IndexDefinition, ManagedIndex, String, NodeTypes.Supplier, NodeTypePredicate, IndexFeedback)}
  methods.
  </p>
  
  @param defn the definition of the index; never null
  @param workspaceName the name of the actual workspace to which the new index applies; never null
  @param nodeTypesSupplier the supplier for the current node types cache; never null
  @param matcher the node type matcher used to determine which nodes should be included in the index, and which automatically
  updates when node types are changed in the repository; may not be null
  @return a {@link ManagedIndexBuilder} instance, or {@code null} (the default) which indicates that a provider chooses to
  ovveride both the createIndex and updateIndex methods.