R 文本挖掘示例在 iconv 上失败

问：

我在 Window 上使用 R4.2.2，我正在尝试在这里完成文本挖掘示例： https://medium.com/@SAPCAI/text-clustering-with-r-an-introduction-for-data-scientists-c406e7454e76

它在此行上失败：

corpus.cleaned <- tm::tm_map(corpus, function(x) iconv(x, to='UTF-8-MAC', sub='byte')) 

有错误消息：

Error in iconv(x, to = "UTF-8-MAC", sub = "byte") : unsupported conversion from '' to 'UTF-8-MAC' in codepage 65001

我不能忽略它，因为它会在示例的后续代码中引起问题：

tdm <- tm::DocumentTermMatrix(corpus.cleaned)
Error in tolower(txt) : invalid input 'RT @MelindaBeckWSJ: ACA has expand coverag to millions, but what that means--and what it has cost--vari widely. We tell 10 stories-141�' in 'utf8towcs'

如何解决此UTF-8-MAC问题？