question: returns the string representing a null value from the data source . concode_field_sep String nullvalue concode_elem_sep Format cachedFormat concode_elem_sep DataSource datasource concode_elem_sep Object cachedValue concode_elem_sep Format format concode_elem_sep String cachedResult concode_field_sep void setNullValue concode_elem_sep Object getValue concode_elem_sep DataSource getDataSource concode_elem_sep void setFormatter concode_elem_sep FormatSpecification getFormatString concode_elem_sep void invalidateCache concode_elem_sep FormatFilter clone concode_elem_sep Object getRawValue concode_elem_sep void setDataSource concode_elem_sep Format getFormatter
target: String function ( ) { return nullvalue ; }