return null;
        }

        String parentPath = childModel.getParent().getRelativePath();

        if (parentPath == null || parentPath.isEmpty()) {
            return null;
        }

        if (source instanceof ModelSource3) {
            return ((ModelSource3) source).getRelatedSource(modelProcessor, parentPath);
        } else {

    }

    private ModelSource getParentPomFile(Model childModel, ModelSource source) {
        String parentPath = childModel.getParent().getRelativePath();
        if (parentPath == null || parentPath.isEmpty()) {
            return null;
        } else {
            return source.resolve(modelProcessor::locateExistingPom, parentPath);
        }
    }

    private ModelData readParentExternally(

// stdVendor returns the canonical import path for the package with the given
// path when imported from the standard-library package at parentPath.
func (ld *loader) stdVendor(parentPath, path string) string {
	if search.IsStandardImportPath(path) {
		return path
	}

	if str.HasPathPrefix(parentPath, "cmd") {
		if !ld.VendorModulesInGOROOTSrc || !MainModules.Contains("cmd") {
			vendorPath := pathpkg.Join("cmd", "vendor", path)

			return errVersionChange
		}
		return nil
	}

	_, pkgs := modload.LoadPackages(ctx, opts, patterns...)
	for _, path := range pkgs {
		const (
			parentPath  = ""
			parentIsStd = false
		)
		_, _, err := modload.Lookup(parentPath, parentIsStd, path)
		if err == nil {
			continue
		}
		if errors.Is(err, errVersionChange) {
			// We already added candidates during loading.
			continue