code: public DescribeFileSystemsRequest withFileSystemIds(String... fileSystemIds) {
          if (this.fileSystemIds == null) {
              setFileSystemIds(new java.util.ArrayList<String>(fileSystemIds.length));
          }
          for (String ele : fileSystemIds) {
              this.fileSystemIds.add(ele);
          }
          return this;
      }
docs: <p>
  (Optional) IDs of the file systems whose descriptions you want to retrieve (String).
  </p>
  <p>
  <b>NOTE:</b> This method appends the values to the existing list (if any). Use
  {@link #setFileSystemIds(java.util.Collection)} or {@link #withFileSystemIds(java.util.Collection)} if you want
  to override the existing values.
  </p>
  
  @param fileSystemIds
  (Optional) IDs of the file systems whose descriptions you want to retrieve (String).
  @return Returns a reference to this object so that method calls can be chained together.