code: public <T extends CharSequence> T validIndex(final T chars, final int index) {
          return validIndex(chars, index, DEFAULT_VALID_INDEX_CHAR_SEQUENCE_EX_MESSAGE, index);
      }
docs: <p>Validates that the index is within the bounds of the argument character sequence; otherwise throwing an exception.</p>
  <pre>Validate.validIndex(myStr, 2);</pre>
  <p>If the character sequence is {@code null}, then the message of the exception is &quot;The validated object is null&quot;.</p><p>If the index is invalid, then the message of the exception is
  &quot;The validated character sequence index is invalid: &quot; followed by the index.</p>
  
  @param <T>
  the character sequence type
  @param chars
  the character sequence to check, validated not null by this method
  @param index
  the index to check
  
  @return the validated character sequence (never {@code null} for method chaining)
  
  @throws NullPointerValidationException
  if the character sequence is {@code null}
  @throws IndexOutOfBoundsException
  if the index is invalid
  @see #validIndex(CharSequence, int, String, Object...)