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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def normalise_filled(self, meta, val):
 """Only care about valid image names"""

        available = list(meta.everything["images"].keys())
        val = sb.formatted(sb.string_spec(), formatter=MergedOptionStringFormatter).normalise(meta, val)
        if val not in available:
            raise BadConfiguration("Specified image doesn't exist", specified=val, available=available)
        return val