default int indexOf(final Object element, final int start, final int end) {
		return element != null
			? indexWhere(element::equals, start, end)
			: indexWhere(Objects::isNull, start, end);
	}
Returns the index of the first occurrence of the specified element
in this sequence, or -1 if this sequence does not contain the element.

@param element element to search for, can be {@code null}
@param start the start index (inclusively) for the element search.
@param end the end index (exclusively) for the element search.
@return the index of the first occurrence of the specified element in
         this sequence, or -1 if this sequence does not contain the element
@throws IndexOutOfBoundsException for an illegal end point index value
         ({@code start < 0 || end > length() || start > end}).
jenetics/src/main/java/io/jenetics/util/Seq.java