Bug 199714 NPE with invalid url[0002]
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/context/ViewerAttributeBean.java
String exprVarName = tempName + "_" 
									+ IBirtConstants.PROP_EXPR;
							ConfigVariable exprVar = handle
									.findConfigVariable( exprVarName );
							String cachedExpr = null;
							if ( exprVar != null )
								cachedExpr = exprVar.getValue( );
							if ( cachedExpr == null )
								cachedExpr = ""; 
							String expr = parameter.getValueExpr( );
							if ( expr == null )
								expr = ""; 
							
							if ( !cachedExpr.equals( expr ) )
								continue;
							
							if ( varName.toLowerCase( ).startsWith(
									ParameterAccessor.PARAM_ISNULL ) )
							{
								this.configMap.put( paramName, null );
							}
							
							else if ( ( displayTextParam = ParameterAccessor
									.isDisplayText( varName ) ) != null )
							{
								this.displayTexts.put( paramName, varValue );
							}
							else
							{
								this.configMap.put( paramName, varValue );