udunits/src/main/java/ucar/units/UnitDBImpl.java
private final void addBySymbol(final String symbol, final Unit newUnit)
			throws UnitExistsException {
		if (symbol != null) {
			addUnique(symbolMap, symbol, newUnit);
		}
	}
private final void addBySymbol(final String symbol, final Unit newUnit)
			throws UnitExistsException {
		if (symbol != null) {
			addUnique(symbolMap, symbol, newUnit);
		}
	}
Adds a unit to the database by symbol.

@param symbol
The symbol for the unit. If <code>null</code> then the unit is
not added.
@param newUnit
The unit to be added.
@throws UnitExistsException
Attempt to redefine an existing unit.