code: public static DefaultValueFunction defaultValue(String fieldName, Object defaultValue) {
  
  		Assert.hasText(fieldName, "Fieldname must not be 'empty' for default value operation.");
  		Assert.notNull(defaultValue, "DefaultValue must not be 'null'.");
  
  		return defaultValue(new SimpleField(fieldName), defaultValue);
  	}
docs: Creates new {@link DefaultValueFunction} representing {@code def(fieldname, defaultValue))}
  
  @param fieldName must not be empty
  @param defaultValue must not be null
  @return