title: The method withValueSerde() in the type Materialized<> is not applicable
body: <p>I am grouping a stream by key and and trying to aggregate the values by the grouped key. I am following the <a href="https://docs.confluent.io/current/streams/developer-guide/dsl-api.html#streams-developer-guide-dsl-aggregating" rel="noreferrer">streams-developer-guide</a></p>
  
  <p>I am getting an error on <code>withValueSerde</code>. It says:</p>
  
  <p><code>The method withValueSerde(Serde&lt;Object&gt;) in the type Materialized&lt;Object,Object,StateStore&gt; is not applicable for the arguments (Serde&lt;Long&gt;)</code></p>
  
  <p><strong>Code:</strong></p>
  
  <pre><code>KStream&lt;String, String&gt; inputStream = builder.stream("input_topic");
  KStream&lt;String, Integer&gt; transformedStream = inputStream.map(
          (key, value) -&gt;  KeyValue.pair(getKey(value), getValue(value)));
  
  KGroupedStream&lt;String, Integer&gt; groupedStream = transformedStream.groupByKey();
  
  KTable&lt;String, Long&gt; aggregatedStream = groupedStream.aggregate(() -&gt; 0L,
          (aggKey, newValue, aggValue) -&gt; aggValue + newValue,
          Materialized.as("aggregated-stream-store").withValueSerde(Serdes.Long()));
  </code></pre>