code: public ScanSpec withNameMap(Map<String, String> nameMap) {
          if (nameMap == null)
              this.nameMap = null;
          else
              this.nameMap = Collections.unmodifiableMap(new LinkedHashMap<String, String>(nameMap));
          return this;
      }
docs: Applicable only when an expression has been specified.
  Used to specify the actual values for the attribute-name placeholders,
  where the value in the map can either be string for simple attribute
  name, or a JSON path expression.
  
  @see ScanRequest#withExpressionAttributeNames(Map)