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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 imageSchema(self):
 """ Returns the image schema. :return: a :class:`StructType` with a single column of images named "image" (nullable) and having the same type returned by :meth:`columnSchema`. .. versionadded:: 2.3.0 """


        if self._imageSchema is None:
            ctx = SparkContext._active_spark_context
            jschema = ctx._jvm.org.apache.spark.ml.image.ImageSchema.imageSchema()
            self._imageSchema = _parse_datatype_json_string(jschema.json())
        return self._imageSchema