Does df.fillNa() turn on { inplace: true } by default?

[Getting Started - Danfo.js] section "Filling missing values in specific columns with specific values:"

const dfd = require("danfojs-node")

let data = {
"Name": ["Apples", "Mango", "Banana", NaN],
"Count": [NaN, 5, NaN, 10],
"Price": [200, 300, 40, 250]
}

let df = new dfd.DataFrame(data)
df.print()

let df_filled = df.fillNa(["Apples", df["Count"].mean()], { columns: ["Name", "Count"] })
df_filled.print()

if we try df.print() again, it is the same as df_filled? So, df.fillNa() turn on { inplace: true } by default? Is this normal?

Thank you