One thing I noticed: this must have happend with an older version of the SPI because line 108 of PrometheusExporter.java (as seen in the logs) points to a comment: https://github.com/aerogear/keycloak-metrics-spi/blob/master/src/main/java/org/jboss/aerogear/keycloak/metrics/PrometheusExporter.java#L108

But we should probably check if resource type is null here: https://github.com/aerogear/keycloak-metrics-spi/blob/master/src/main/java/org/jboss/aerogear/keycloak/metrics/PrometheusExporter.java#L114