public void validate(String exp) {
        Preconditions.checkNotNull(scopeType, exp + ": one of service(), instance() or endpoint() should be invoke");
    }
Validate context after parsing
@param exp expression literal
oap-server/analyzer/meter-analyzer/src/main/java/org/apache/skywalking/oap/meter/analyzer/dsl/ExpressionParsingContext.java