Error parsing negative numbers in decision table

Compiling attached .xls table results in exception, K12 column contains "-1". This worked in drools 5.0.1

org.drools.template.parser.DecisionTableParseException: Priority is not an integer literal, in cell K12
at org.drools.decisiontable.parser.DefaultRuleSheetListener.nextDataCell(DefaultRuleSheetListener.java:607)
at org.drools.decisiontable.parser.DefaultRuleSheetListener.processRuleCell(DefaultRuleSheetListener.java:456)
at org.drools.decisiontable.parser.DefaultRuleSheetListener.newCell(DefaultRuleSheetListener.java:327)
at org.drools.decisiontable.parser.xls.ExcelParser.newCell(ExcelParser.java:187)
at org.drools.decisiontable.parser.xls.ExcelParser.processSheet(ExcelParser.java:138)
at org.drools.decisiontable.parser.xls.ExcelParser.parseFile(ExcelParser.java:82)
at org.drools.decisiontable.SpreadsheetCompiler.compile(SpreadsheetCompiler.java:93)
at org.drools.decisiontable.SpreadsheetCompiler.compile(SpreadsheetCompiler.java:72)
at com.piag.Bundler.buildPackage(Bundler.java:106)
at com.piag.Bundler.main(Bundler.java:69)