Don't store GCP Metrics in variable

nuxeo_1          | 2021-08-15T07:50:26,295 WARN  [EnrichingStreamProcessor] Enrichment error (gcp.imageCropHints) for record: Record{watermark=213518096595288064, wmDate=2021-08-15 07:49:58.487, flags=[DEFAULT], key='b58ed764-4c18-4369-aa63-fa79c37c940c', data.length=470, data="{"blobTypes":{"picture:views/3/content":"img"},"blobs":{"picture:views/3/content":{"mimeType":"image/jpeg","encoding":null,"dig"}
nuxeo_1          | java.lang.NullPointerException: null
nuxeo_1          |      at org.nuxeo.ai.gcp.provider.AbstractTagProvider.registerMetrics(AbstractTagProvider.java:134) ~[nuxeo-ai-gcp-core-3.1.2-2021.jar:?]
nuxeo_1          |      at org.nuxeo.ai.gcp.provider.AbstractTagProvider.enrich(AbstractTagProvider.java:121) ~[nuxeo-ai-gcp-core-3.1.2-2021.jar:?]
nuxeo_1          |      at org.nuxeo.ai.enrichment.EnrichingStreamProcessor$EnrichmentComputation.getAiMetadata(EnrichingStreamProcessor.java:247) ~[nuxeo-ai-core-3.1.2-2021.jar:?]
nuxeo_1          |      at org.nuxeo.ai.enrichment.EnrichingStreamProcessor$EnrichmentComputation.lambda$getProvider$5(EnrichingStreamProcessor.java:235) ~[nuxeo-ai-core-3.1.2-2021.jar:?]