code: @Nullable
      public boolean addModuleSpec(ModuleSpec moduleSpec) {
          Objects.requireNonNull(moduleSpec, "moduleSpec");
          ModuleIdentifier revisionId = moduleSpec.getModuleIdentifier();
          boolean available = !moduleSpecs.containsKey(revisionId);
          if (available) {
              moduleSpecs.put(revisionId, moduleSpec);
          }
          return available;
      }
docs: Add a {@link ModuleSpec} to the internal repository making it ready to load. Note, this doesn't
  actually load the {@link Module}.
  @see #loadModule(ModuleIdentifier)
  
  @param moduleSpec spec to add
  @return true if the instance was added