This function is named to look like a test and has a return value like a test, but it is not a test and its return value is ignored.
It is a conditional mutator function.
Rename/replace with private void cloneUniqueSubqueryPartitionExpression() or cloneSubqueryPartitionExpressionIfUnique() or if you don't like "unique" cloneSubqueryPartitionExpressionIfOnlyOne()