Empty values of correlation matrix cause problen in knitting table on word document

You can try this (don't forget to remove redundant libs, if you don't use it):

---
output:
  word_document: default
---


```{r setup, include=FALSE}
library(magrittr)
library(flextable)
library(data.table)
```

```{r,echo=F}
tab<-structure(list(V1 = c("", "", "", "", "", "", "", "", "", ""), 
    V2 = c("-.21**", "", "", "", "", "", "", "", "", ""), V3 = c(".09", 
    "-.03", "", "", "", "", "", "", "", ""), V4 = c("-.23***", 
    ".18**", ".15*", "", "", "", "", "", "", ""), V5 = c(".01", 
    ".07", "-.03", "-.12", "", "", "", "", "", ""), V6 = c(".08", 
    "-.07", ".29***", ".12", "-.22***", "", "", "", "", ""), 
    V7 = c("-.09", ".21**", "-.02", ".13*", ".68***", "-.12", 
    "", "", "", ""), V8 = c(".17*", ".25***", ".05", "-.01", 
    ".32***", ".13*", ".25***", "", "", ""), V9 = c(".16*", "-.20**", 
    ".29***", "-.10", ".08", ".14*", ".01", ".17**", "", ""), 
    V10 = c("-.31***", ".14*", "-.26***", ".05", "-.08", "-.20**", 
    ".02", "-.15*", "-.36***", ""), V11 = c("-.02", "-.13*", 
    "-.29***", "-.06", ".05", "-.05", ".07", "-.08", "-.23***", 
    ".26***"), V12 = c(".03", "-.02", ".29***", ".02", "-.09", 
    ".11", "-.07", ".12", ".20**", "-.32***"), V13 = c("-.10", 
    ".00", ".15*", "-.08", ".00", ".01", ".02", "-.02", ".01", 
    ".10"), V14 = c(".03", "-.17**", "-.15*", "-.09", ".01", 
    ".03", "-.10", "-.26***", "-.04", ".08"), V15 = c(".32***", 
    "-.33***", ".32***", "-.31***", "-.07", ".21**", "-.13", 
    "-.07", ".18**", "-.39***"), V16 = c(".25***", ".00", "-.09", 
    "-.20**", ".01", ".08", ".04", "-.02", "-.21**", "-.15*")), row.names = c("all_fear_fail", 
"all_high_stat_entre", "patience", "risktaking", "posrecip", "negrecip", "altruism", "trust_gps", "lrgdpch2005", "gini_net2000"
), class = "data.frame")

tab1 <- data.table(tab, keep.rownames = TRUE)

tab1 %>% 
  flextable() %>% 
  align(part = "all") %>% # left align
  set_caption(caption = "Example") %>% 
  font(fontname = "Calibri (Body)", part = "all") %>% 
  fontsize(size = 9, part = "all") %>% 
  # add footer if you want
  # add_footer_row(values = "* p < 0.05. ** p < 0.01. *** p < 0.001.", 
  #                colwidths = 4) %>% 
  theme_booktabs() %>% # default theme
  fit_to_width(max_width = 8)
```