[Python] Plot and annotate NaN values in a seaborn heatmap

I have a Seaborn heatmap based on a DataFrame containing some NaN values. The heatmap turns out to just have those cells blank. However, I would like a custom color, e.g., light grey to be drawn with an 'NaN' annotation. How can I achieve this?

import seaborn as sns
import matplotlib.pyplot as plt
from matplotlib.colors import LogNorm, Normalize
import numpy as np
import pandas as pd

data = {
"Server (%)": [np.nan, 0.2, 2.4],
"Scheduler (%)": [np.nan, 2.3, 4.5]
}
merged_summary = pd.DataFrame(data)

# Prepare annotation matrix
annot = merged_summary.copy()
for i in range(annot.shape[0]):
for j in range(annot.shape[1]):
val = annot.iat[i, j]
if pd.isna(val):
annot.iat[i, j] = "N/A"
elif val > 1:
annot.iat[i, j] = f"{val:.1f} %"
else:
annot.iat[i, j] = f"{val:.3f} %"

fig, ax = plt.subplots(3,1, figsize=(5,7), constrained_layout=True)
h2 = sns.heatmap(
data=merged_summary,
annot=annot.values,
fmt='',
cmap="coolwarm",
cbar=False,
linewidths=0.5,
linecolor='white',
mask=merged_summary.isna(),
vmin=0.1,
vmax=30,
norm=LogNorm(vmin=0.1, vmax=30),
annot_kws={"size": 8},
ax=ax[2],
)
plt.show()




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