I found this source code: Series. Your Form class extends this Series class.
If parameter 'abc' not exists, then null (defaultValue) will be returned:
public String getFirstValue(String name) {
return getFirstValue(name, false);
}
public String getFirstValue(String name, boolean ignoreCase) {
return getFirstValue(name, ignoreCase, null);
}
public String getFirstValue(String name, boolean ignoreCase, String defaultValue) {
String result = defaultValue;
NamedValue<String> param = getFirst(name, ignoreCase);
if ((param != null) && (param.getValue() != null)) {
result = param.getValue();
}
return result;
}