code: public Key withAttribute(String attributeName, AttributeValue value) {
          if (this.attributes == null) {
              this.attributes = new HashMap<String, AttributeValue>();
          }
          attributes.put(attributeName, value);
          return this;
      }
docs: The method set attribute name and attribute value with input parameters for a key.
  Returns a reference to this object so that method calls can be chained together.
  
  @param attributeName The attribute name to set for a key.
  @param value The attribute value to set for a key.
  @return A reference to this object so that method calls can be chained together.