public static Path resolveStroomDocsFile(final Path subPath) {
        final String stroomDocsRepoDirStr = System.getProperty(STROOM_DOCS_REPO_DIR_PROP_KEY);
        final Path stroomDocsRepoDir;

        if (NullSafe.isBlankString(stroomDocsRepoDirStr)) {
            final Path stroomRepoRoot = ProjectPathUtil.getRepoRoot();
            stroomDocsRepoDir = stroomRepoRoot.getParent()
                    .resolve("stroom-docs");
        } else {
            stroomDocsRepoDir = Paths.get(stroomDocsRepoDirStr);
        }
        if (!Files.isDirectory(stroomDocsRepoDir)) {
            throw new RuntimeException(LogUtil.message(
                    "stroom-docs dir '{}' does not exist. " +
                    "Expecting it to be a sibling of this stroom repo. If that is not the case, either " +
                    "conform or set the system prop '{}' to the location of your stroom-docs repo.",
                    stroomDocsRepoDir.toAbsolutePath().normalize(),
                    STROOM_DOCS_REPO_DIR_PROP_KEY));
        }

        final Path file = stroomDocsRepoDir.resolve(subPath).toAbsolutePath().normalize();

        if (!Files.isRegularFile(file)) {
            throw new RuntimeException(LogUtil.message("stroom-docs file '{}' does not exist",
                    stroomDocsRepoDir.toAbsolutePath().normalize()));
        }
        return file;
    }
@param subPath A path to a file in the stroom-docs repo that is relative to the
               stroom-docs repo root.
@return An absolute path to the file which has been tested to see if it exists and
is a regular file.
stroom-test-common/src/main/java/stroom/test/common/docs/StroomDocsUtil.java