刚学习drools，这种错误怎么处理啊。
rule "null safe dereferencing"
when
Customer(address != null && address.postalCode == "111")
Customer(address !.postalCode() == "111")
then
System.out.println("Null-safe dereferencing operator");
end

Unable to Analyse Expression address.postalCode:
[Error: unable to resolve method using strict-mode: com.pojo.Address.postalCode(
)]
[Near : {... address.postalCode ....}]
                     ^
[Line: 162, Column: 2] : [Rule name='Null-safe dereferencing operator']

Unable to analyze expression 'address.postalCode' : [Rule name='Null-safe derefe
rencing operator']

Unable to Analyse Expression address.postalCode == "111":
[Error: unable to resolve method using strict-mode: com.pojo.Address.postalCode(
)]
[Near : {... address.postalCode == "111" ....}]
                     ^
[Line: 162, Column: 2] : [Rule name='Null-safe dereferencing operator']

Unable to Analyse Expression address.postalCode:
[Error: unable to resolve method using strict-mode: com.pojo.Address.postalCode(
)]
[Near : {... address.postalCode ....}]
                     ^
[Line: 163, Column: 2] : [Rule name='Null-safe dereferencing operator']

Unable to analyze expression 'address.postalCode' : [Rule name='Null-safe derefe
rencing operator']