code: public void setContentMD5(String md5Base64) {
          if(md5Base64 == null){
              metadata.remove(Headers.CONTENT_MD5);
          }else{
              metadata.put(Headers.CONTENT_MD5, md5Base64);
          }
  
      }
docs: <p>
  Sets the base64 encoded 128-bit MD5 digest of the associated object
  (content - not including headers) according to RFC 1864. This data is
  used as a message integrity check to verify that the data received by
  Amazon S3 is the same data that the caller sent. If set to null,then the
  MD5 digest is removed from the metadata.
  </p>
  <p>
  This field represents the base64 encoded 128-bit MD5 digest digest of an
  object's content as calculated on the caller's side. The ETag metadata
  field sometimes (but not always) represents the hex encoded 128-bit MD5 digest as computed by Amazon
  S3. See the documentation at {@link #getETag()} for more information on what the ETag field represents.
  </p>
  <p>
  The AWS S3 Java client will attempt to calculate this field automatically
  when uploading files to Amazon S3.
  </p>
  
  @param md5Base64
  The base64 encoded MD5 hash of the content for the object
  associated with this metadata.
  
  @see ObjectMetadata#getContentMD5()