static <T> T assertOne(Stream<T> st) {
		return assertOne(st.collect(Collectors.toList()));
	}
Assert that exactly one element is in a stream and get that element

@param <T> the type of element
@param st the stream
@return the element
@throws AssertionError if no element or many elements exist in the stream
Ghidra/Framework/Emulation/src/main/java/generic/Unique.java