liquibase-core/src/main/java/liquibase/util/StringUtil.java
public static String trimToNull(String string) {
        if (string == null) {
            return null;
        }
        String returnString = string.trim();
        if (returnString.isEmpty()) {
            return null;
        } else {
            return returnString;
        }
    }
public static String trimToNull(String string) {
        if (string == null) {
            return null;
        }
        String returnString = string.trim();
        if (returnString.isEmpty()) {
            return null;
        } else {
            return returnString;
        }
    }
Returns the trimmed (left and right) form of the input string. If the string is empty after trimming (or null
was passed in the first place), null is returned, i.e. the input string is reduced to nothing.
@param string the string to trim
@return the trimmed string or null