cdm/src/main/java/thredds/client/catalog/builder/DatasetBuilder.java
public static void addToList(Map<String, Object> flds, String fldName, Object fldValue) {
    if (fldValue == null) return;
    Object prevVal = flds.get(fldName);
    if (prevVal == null) {
      flds.put(fldName, fldValue);
      return;
    }

    List prevList;
    if (prevVal instanceof List) {
      prevList = (List) prevVal;
    } else {
      prevList = new ArrayList(5);
      prevList.add(prevVal);
      flds.put(fldName, prevList);
    }

    if (fldValue instanceof List) {
      prevList.addAll((List) fldValue);
    } else {
      prevList.add(fldValue);
    }
  }
public static void addToList(Map<String, Object> flds, String fldName, Object fldValue) {
    if (fldValue == null) return;
    Object prevVal = flds.get(fldName);
    if (prevVal == null) {
      flds.put(fldName, fldValue);
      return;
    }

    List prevList;
    if (prevVal instanceof List) {
      prevList = (List) prevVal;
    } else {
      prevList = new ArrayList(5);
      prevList.add(prevVal);
      flds.put(fldName, prevList);
    }

    if (fldValue instanceof List) {
      prevList.addAll((List) fldValue);
    } else {
      prevList.add(fldValue);
    }
  }
Utility routine to keep list of objects small.
add fldValue to the fldName list in flds.
fldValue may be a list or an object.
if no list, just keep the object without creating a list (common case).
otherwise add it to the existing list.