R语言计算系统发育多样性

问题遇到的现象和发生背景

计算系统发育多样性时，输入comm.pd<-pd(com_2020,phylo)，
出现Error in UseMethod("is.rooted") :
no applicable method for 'is.rooted' applied to an object of class "NULL"
In addition: Warning message:
In drop.tip(tree, treeabsent) : drop all tips of the tree: returning NULL
请问如何解决，多谢了