default int indexWhere(
		final Predicate<? super T> predicate,
		final int start
	) {
		return indexWhere(predicate, start, length());
	}
<p>
Returns the index of the first element on which the given predicate
returns {@code true}, or -1 if the predicate returns false for every
sequence element.
</p>
{@snippet lang="java":
// Finding index of first null value.
final int index = seq.indexOf(o -> o == null);

// Assert of no null values.
assert (sequence.indexOf(o -> o == null) == -1);
}

@param predicate the search predicate.
@param start the search start index
@return the index of the first element on which the given predicate
         returns {@code true}, or -1 if the predicate returns {@code false}
         for every sequence element.
@throws NullPointerException if the given {@code predicate} is {@code null}.
@throws IndexOutOfBoundsException for an illegal end point index value
         ({@code start < 0 || start > length()}).
jenetics/src/main/java/io/jenetics/util/Seq.java