My heatmap is blank

I am trying to create a heatmap with the follow data: It is a lot of data points, this is just a preview. Any ideas on why it is blank?

       TF         target   importance
0     ZIC5     ZIC2  244.284998
1     DLX6     DLX5  146.211550
2  FOXD4L6  FOXD4L3  139.951544
3    DDX43     OOEP  133.502314
4  FOXD4L3  FOXD4L6  132.367859
5     DLX5     DLX6  131.638314
6    FOXD4  FOXD4L1  128.395748
7   HOXA11   HOXA10  112.056258
8    HOXA2    HOXA3  110.962698
9     ZIC2     ZIC5  109.077028

CODE BELOW:

import os
import glob
import pickle
import pandas as pd
import numpy as np
import scanpy as sc
import loompy as lp

from dask.diagnostics import ProgressBar

from MulticoreTSNE import MulticoreTSNE as TSNE

import seaborn as sns
import matplotlib.pyplot as plt

df = pd.read_csv("adj.tsv", sep='\t')
print(df.head(10))
df = df.pivot("TF", "target", "importance")
hm = sns.heatmap(df, linewidth = 0.5, cmap = 'coolwarm')

Start with the Python snippet, especially the adj.tsv read, DataFrame pivot, and seaborn heatmap call, and reproduce it in the reported Jupyter setup. The input file and environment details are not provided, so first establish whether the blank output is specific to ipympl. Done means a reproducible diagnosis or a clarified report with the missing setup and data details.