Bug 182673 No default value error message prompts incorrectly
Steps to reproduce: 1. New a report parameter; 2. Choose control type as Combo; 3. Choose parameter as dynamic type; Expected result: As the isRequired is false by default, parameter's default value can be null value. There should be no error message about no default value prompt. Actual result; Error messages prompts
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/ui/dialogs/CascadingParametersDialog.java
if ( getDataSetColumns( paramHandle, false ).length > 0 )
							{
								value = LABEL_SELECT_DISPLAY_COLUMN;
							}
							else
							{
								value = LABEL_NO_COLUMN_AVAILABLE;
							}
						}
						break;
					}
				}
			}
			if ( value == null )
			{
				value = ""; 
			}
			return value;
		}
		private String getDummyText( Object element )
		{
			String dummyText = ""; 
			int index = getTableIndex( element );
			for ( int i = 0; i < index; i++ )
			{
				dummyText += "    "; 
			}
			return dummyText;
		}
		public void addListener( ILabelProviderListener listener )