Bug 153412 Change parameter type will cause preview fail
Description: Change parameter type will cause preview fail Steps to reproduce: 1. New a report paramter, string, text-box, default value is abc. 2. Drag the parameter to Layout and preview. 3. Change the parameter's type to integer, list-box, add a value 1 4. Preview Expected result: No errors. Actual result: The value "abc" is invalid with the type "integer".
UI/org.eclipse.birt.report.designer.ui.preview/src/org/eclipse/birt/report/designer/ui/preview/editors/ReportPreviewFormPage.java
{
			for ( int i = 0; i < parameters.size( ); i++ )
			{
				if ( parameters.get( i ) instanceof ScalarParameterHandle )
				{
					ScalarParameterHandle parameter = ( (ScalarParameterHandle) parameters.get( i ) );
					if ( parameter.isHidden( ) )
					{
						continue;
					}
					String paramValue = null;
					if ( params != null
							&& params.containsKey( parameter.getName( ) ) )
					{
						Object curVal = params.get( parameter.getName( ) );
						if ( curVal != null )
							paramValue = curVal.toString( );
					}
					if ( paramValue == null && !parameter.allowNull( ) )
					{
						missingParameter = true;
						break;
					}
					if ( paramValue != null
							&& paramValue.trim( ).length( ) <= 0
							&& !parameter.allowBlank( )
							&& parameter.getDataType( )
									.equalsIgnoreCase( DesignChoiceConstants.PARAM_TYPE_STRING ) )
					{
						missingParameter = true;