code: public TLVElement getFirstChildElement(int tag) {
          for (TLVElement element : children) {
              if (tag == element.getType()) {
                  return element;
              }
          }
          return null;
      }
docs: Returns the first child element with specified tag. If tag doesn't exist then null is returned.
  
  @param tag
  tag to search.
  
  @return The first instance of {@link TLVElement} with specified tag,
  or null when the child element with specified tag doesn't exist.