[docs-infra] Prevent to set undefined as a default value

[alexfauquette]

Why not?

  /**
   * The height of the chart in px. If not defined, it takes the height of the parent element.
   */
  height: PropTypes.number,

It looks funny on the API page:

As far as I know, we only do this if it's null. undefined is the default "prop default value". In #41114 I try to improve its display.

If this change makes sense, then I think we should throw an error in docs-infra when the default is undefined, saying to remove it as redundant, to prevent future regressions.

Originally posted by @oliviertassinari in mui/mui-x#11996 (comment)

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