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/ParameterDialog.java
{
				canFinish = ( errorMessageLine.getImage( ) == null );
			}
			if ( columnChooser != null && !isStatic( ) )
			{
				canFinish &= ( getExpression( columnChooser.getText( ) ) != null );
			}
		}
		getOkButton( ).setEnabled( canFinish );
	}
	private void updateCheckBoxArea( )
	{
		
		if ( DesignChoiceConstants.PARAM_CONTROL_TEXT_BOX.equals( getSelectedControlType( ) ) )
		{
			doNotEcho.setEnabled( true );
		}
		else
		{
			doNotEcho.setEnabled( false );
		}
		
		if ( DesignChoiceConstants.PARAM_CONTROL_TEXT_BOX.equals( getSelectedControlType( ) )
				|| DesignChoiceConstants.PARAM_CONTROL_CHECK_BOX.equals( getSelectedControlType( ) )
				|| !isStatic( ) )
		{
			needSort.setEnabled( false );
		}
		else
		{