liquibase-core/src/main/java/liquibase/change/ColumnConfig.java
public ColumnConfig setDefaultValueDate(String defaultValueDate) {
        defaultValueDate = StringUtil.trimToNull(defaultValueDate);
        if ((defaultValueDate == null) || "null".equalsIgnoreCase(defaultValueDate)) {
            this.defaultValueDate = null;
        } else {
            try {
                this.defaultValueDate = new ISODateFormat().parse(defaultValueDate);
            } catch (ParseException e) {
                //probably a computed date
                this.defaultValueComputed = new DatabaseFunction(defaultValueDate);
            }
        }

        return this;
    }
public ColumnConfig setDefaultValueDate(String defaultValueDate) {
        defaultValueDate = StringUtil.trimToNull(defaultValueDate);
        if ((defaultValueDate == null) || "null".equalsIgnoreCase(defaultValueDate)) {
            this.defaultValueDate = null;
        } else {
            try {
                this.defaultValueDate = new ISODateFormat().parse(defaultValueDate);
            } catch (ParseException e) {
                //probably a computed date
                this.defaultValueComputed = new DatabaseFunction(defaultValueDate);
            }
        }

        return this;
    }
Set the date this column should default to. Supports any of the date or datetime formats handled by {@link ISODateFormat}.
If the passed value cannot be parsed as a date, it is assumed to be a function that returns a date.
If the string "null" or an empty string is passed, it will set a null value.