public static CharSequence subSequence(CharSequence cs, int start) {
        return cs == null ? null : cs.subSequence(start, cs.length());
    }
<p>Returns a new {@code CharSequence} that is a subsequence of this
sequence starting with the {@code char} value at the specified index.</p>

<p>This provides the {@code CharSequence} equivalent to {@link String#substring(int)}.
The length (in {@code char}) of the returned sequence is {@code length() - start},
so if {@code start == end} then an empty sequence is returned.</p>

@param cs  the specified subsequence, null returns null
@param start  the start index, inclusive, valid
@return a new subsequence, may be null
@throws IndexOutOfBoundsException if {@code start} is negative or if 
 {@code start} is greater than {@code length()}
android/android_framework/base/src/main/java/lang3/CharSequenceUtils.java