code: @Nullable
      public ModuleSpec getModuleSpec(ModuleIdentifier revisionId) {
          Objects.requireNonNull(revisionId, "revisionId");
          return moduleSpecs.get(revisionId);
      }
docs: Get a {@link ModuleSpec} that was added to this instance
  @param revisionId id to search for
  @return the instance associated with the given revisionIds