Bug 6233 keep property value if IPropertySource.getEditableValue returns null
If IPropertySource is appearing in the property sheet as the value of a property of some other IPropertySource then the source is asked for getEditableValue. If the returned value is null, then the PropertySheetEntry should use the original value, and not null value. For example, my PropertySource contains a property with value of type jdt.IType. The PropertySource for IType returns null in getEditableValue, and this null is actually used by PropertySheetEntry as the edit value; the consequence is that CellEditor provided in PropertyDescriptor of the property does not work. @see PropertySheetEntry#getEditValue
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/JavaElementProperties.java
public JavaElementProperties(IJavaElement source) {
		fSource= source;
	}
	
	public IPropertyDescriptor[] getPropertyDescriptors() {
		return fgPropertyDescriptors;
	}
	
	public Object getPropertyValue(Object name) {
		if (name.equals(IBasicPropertyConstants.P_TEXT)) {
			return fSource.getElementName();
		}
		return null;
	}
	
	public void setPropertyValue(Object name, Object value) {
	}
	
	public Object getEditableValue() {
		return null;
	}
	
	public boolean isPropertySet(Object property) {
		return false;
	}
	
	public void resetPropertyValue(Object property) {
	}
}