code: function doCacheForMethod (signature) {
      // validate signature
      signature = getValidSignature(signature)
      // if method is not defined do nothing
      if (!hasMethod(signature.signature)) {
          return
      }
      // get method and module
      var method = getMethod(signature.signature)
      var module = getModule(signature.moduleName)
      // skip if no caches for module
      if (!defined(immutable.caches[signature.moduleName])) {
          return
      }
      // skip if no caches for method
      if (!defined(immutable.caches[signature.moduleName][signature.methodName])) {
          return
      }
      // get cache entry
      var cache = immutable.caches[signature.moduleName][signature.methodName]
      // set cache rule on method
      module.cache(signature.methodName, cache.cache)
      // set cached flag true now that cache rule added
      cache.cached = true
  }
docs: @function doCacheForMethod
  
  @param {string} signature - moduleName.functionName to set cache rule for
  
  @throws {Error}