code: private String getExpressionAttributeName(String association, String attributeName) {
          StringBuilder sb = new StringBuilder();
  
          if (association.contains(".")) {
              String[] associationParts = association.split(".");
  
              for (String associationPart : associationParts) {
                  sb.append(getExpressionAttributeName(associationPart));
                  sb.append('.');
              }
          } else {
              sb.append(getExpressionAttributeName(association));
              sb.append('.');
          }
  
          return sb.append(getExpressionAttributeName(attributeName)).toString();
      }
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