private function getEntityIdentifierAspectValue( $source, $evaluationResult, $log )
	{

		// Get the entity identifier from the source
		if ( is_null( $this->entityIdentifierRule ) )
		{
			$context = $this->getContextForSource( $source, $evaluationResult, ASPECT_ENTITY_IDENTIFIER, $log, $contextRef );
			if ( ! $context || is_null( $context['entity']['identifier'] ) ) return null;

			// TODO What is in the $context array
			return $context['entity']['identifier'];
		}
		else
		{
			/**
			 * @var EntityIdentifier $identifier
			 */
			$identifier = EntityIdentifier::fromArray( $this->entityIdentifierRule );
			// This function will throw an exception if there is a problem so there is no return value to check
			$this->checkSAVConflicts( $identifier->source, ASPECT_ENTITY_IDENTIFIER, $evaluationResult, $log );
			return $identifier->getValue( $this, $evaluationResult, $log );
		}

	}