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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 make_roi(cls, sources=None):
 """Build and return a `fermipy.roi_model.ROIModel` object from a dict with information about the sources """

        if sources is None:
            sources = {}
        src_fact = cls()
        src_fact.add_sources(sources)
        ret_model = roi_model.ROIModel(
            {}, skydir=SkyCoord(0.0, 0.0, unit='deg'))
        for source in src_fact.sources.values():
            ret_model.load_source(source,
                                  build_index=False, merge_sources=False)
        return ret_model