R - Error in if (nrow(M) == 2) { : argument is of length zero

In following code:

    det<-function(M)
    {
        if (nrow(M) == 2)
        {
            return(M[1,1]*M[2,2]-M[1,2]*M[2,1])
        }
        else
        {
          d<-0
          for (i in 1:ncol(M))
          {
            d<-d+(-1)^(i+1)*M[1][i]*det(M[-1,i])
          }
          return(d)
       }
    }

to execute function I determined x<-matrix(c(1:9),nrow=3) when execute the function det(x) I get error: Error in if (nrow(M) == 2) { : argument is of length zero