code: public static StringExpression asString(Expression<String> expr) {
          Expression<String> underlyingMixin = ExpressionUtils.extract(expr);
          if (underlyingMixin instanceof PathImpl) {
              return new StringPath((PathImpl<String>) underlyingMixin);
          } else if (underlyingMixin instanceof OperationImpl) {
              return new StringOperation((OperationImpl<String>) underlyingMixin);
          } else if (underlyingMixin instanceof TemplateExpressionImpl) {
              return new StringTemplate((TemplateExpressionImpl<String>) underlyingMixin);
          } else {
              return new StringExpression(underlyingMixin) {
  
                  private static final long serialVersionUID = 8007203530480765244L;
  
                  @Override
                  public <R, C> R accept(Visitor<R, C> v, C context) {
                      return this.mixin.accept(v, context);
                  }
  
              };
          }
      }
docs: Create a new StringExpression
  
  @param expr Expression of type String
  @return new StringExpression