true when a valid surrogate pair starts at the given index in the given string . out-of-range indexes return false . concode_field_sep PlaceHolder placeHolder concode_field_sep String nullToEmpty concode_elem_sep String padStart concode_elem_sep String commonPrefix concode_elem_sep boolean isNullOrEmpty concode_elem_sep String repeat concode_elem_sep String commonSuffix concode_elem_sep String emptyToNull concode_elem_sep String padEnd