cdm/src/main/java/ucar/nc2/NetcdfFileWriter.java
public Dimension addDimension(String dimName, int length) {
    return addDimension(null, dimName, length, false, false);
  }
public Dimension addDimension(String dimName, int length) {
    return addDimension(null, dimName, length, false, false);
  }
// use these calls in define mode