code: public boolean recordReturnType(JSTypeExpression jsType) {
      if (jsType != null && currentInfo.getReturnType() == null
          && !hasAnySingletonTypeTags()) {
        currentInfo.setReturnType(jsType);
        populated = true;
        return true;
      } else {
        return false;
      }
    }
docs: Records a return type.
  
  @return {@code true} if the return type was recorded and {@code false} if
  it is invalid or was already defined