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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 _get_default_projection(cls):
 		"""Construct the default projection document."""

		
		projected = []  # The fields explicitly requested for inclusion.
		neutral = []  # Fields returning neutral (None) status.
		omitted = False  # Have any fields been explicitly omitted?
		
		for name, field in cls.__fields__.items():
			if field.project is None:
				neutral.append(name)
			elif field.project:
				projected.append(name)
			else:
				omitted = True
		
		if not projected and not omitted:
			# No preferences specified.
			return None
			
		elif not projected and omitted:
			# No positive inclusions given, but negative ones were.
			projected = neutral
		
		return {field: True for field in projected}