R语言报错 unable to find an inherited method for function ‘assays’ for signature ‘"data.frame"’

问题遇到的现象和发生背景

下载处理TCGA miRNA数据时报错

问题相关代码，请勿粘贴截图

####下载mRNA+lncRNA表达数据
setwd("C:\\Users\\ddddddd\\Desktop\\新建文件夹")
BiocManager::install("TCGAbiolinks")
library(TCGAbiolinks)
##下载miRNA数据
expquery = GDCquery(project = "TCGA-LAML", 
                 legacy = FALSE, 
                 data.category = "Transcriptome Profiling", 
                 data.type = "miRNA Expression Quantification", 
                 workflow.type = "BCGSC miRNA Profiling")
GDCdownload(expquery)
expquery2 <- GDCprepare(expquery)
expMatrix <- TCGAanalyze_Preprocessing(expquery2)

运行结果及报错内容

最后一步报错：Error in (function (classes, fdef, mtable) :
unable to find an inherited method for function ‘assays’ for signature ‘"data.frame"’

我的解答思路和尝试过的方法

不知道怎么解决

我想要达到的结果

求解决方法