Bug 127861 [DataBinding] Mark API provisional
bundles/org.eclipse.jface.databinding/src/org/eclipse/jface/databinding/converterfunction/ConversionFunctionRegistry.java
* @return An appropriate IConversionFunction or TheNullConverter.NULL on error
     */
    public static IConversionFunction get(Class sourceClass, Class destClass) {
        if (sourceClass.equals(destClass))
            return TheIdentityFunction.IDENTITY;
        
        HashMap sourceClassConverters = (HashMap) converterFunctions.get(sourceClass);
        
        if (sourceClassConverters == null) {
            System.err.println("No converters for pair (" + sourceClass + ", " + destClass + ") have been registered"); 
            return TheNullStringFunction.NULL;
        }
        
        IConversionFunction result = (IConversionFunction) sourceClassConverters.get(destClass);
        
        if (result == null) {
        	System.err.println("No converters for pair (" + sourceClass + ", " + destClass + ") have been registered"); 
            return TheNullStringFunction.NULL;
        }
        
        return result;
    }
    
    /**
     * Returns if there is a converter registered for a specific class2class
     * conversion.
     *  
     * @param sourceClass
     * @param destClass
     * @return true if a converter is registered; false otherwise.