The message "font family 'serif' not found" is reported by Matplotlib.

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This error message is related to the use of fonts in Matplotlib. When Matplotlib cannot find the specified font family, it will return this error message. The font family 'serif' is a general classification of fonts that includes Times New Roman, Georgia, and other similar fonts. To fix this error, you can try installing the missing font or specifying a different font family in your Matplotlib code. You can also use the default font family by omitting the font specification in your code.