code: private File getProjectDir(String projectId, boolean create) throws IOException {
          File projectDir = new File(getKeenCacheDirectory(), projectId);
          if (create && !projectDir.exists()) {
              KeenLogging.log("Cache directory for project '" + projectId + "' doesn't exist. " +
                      "Creating it.");
              if (!projectDir.mkdirs()) {
                  throw new IOException("Could not create project cache directory '" +
                          projectDir.getAbsolutePath() + "'");
              }
          }
          return projectDir;
      }
docs: Gets the cache directory for the given project. Optionally creates the directory if it
  doesn't exist.
  
  @param projectId The project ID.
  @return The cache directory for the project.
  @throws IOException