Minimum working example for seq.clamp() error

my_dat.nex

#NEXUS

Begin data;
Dimensions ntax=3 nchar=5;
Format datatype=DNA missing=? gap=-;
Matrix
A   CTGAA
B   TCCCG
C   CAAAC
;
End;

my_error.Rev

# RevBayes reports the following error
#
# Error:	Argument or label mismatch for function call 'clamp' with arguments ( TimeTree<constant>).
#   Correct usage is:
#   clamp (AbstractHomologousDiscreteCharacterData<any> x)
#
          
# read alignment
dat = readDiscreteCharacterData("my_dat.nex")

# read tree
phy = readTrees("my_phy.tre")[1]

# build rate matrix
Q <- fnJC(4)

# create phylogenetic CTMC
seq ~ dnPhyloCTMC(tree=phy,
                  Q=Q,
                  type="DNA",
                  nSites=dat.nchar())


# NOTE: this is when I get the error!
# clamp the tree to seq
seq.clamp(phy)

my_phy.tre

((A:1,B:1):1,C:2);