Try Object.class if cannot get persistent entity for class.

src/main/java/org/springframework/data/couchbase/core/convert/MappingCouchbaseConverter.java

@@ -20,6 +20,7 @@
 import static org.springframework.data.couchbase.core.mapping.id.GenerationStrategy.USE_ATTRIBUTES;
 
 import java.beans.Transient;
+import java.lang.reflect.InaccessibleObjectException;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -982,7 +983,16 @@ public <R> R readValue(Object value, CouchbasePersistentProperty prop, Object pa
 
 	private ConvertingPropertyAccessor<Object> getPropertyAccessor(Object source) {
 
-		CouchbasePersistentEntity<?> entity = mappingContext.getRequiredPersistentEntity(source.getClass());
+		CouchbasePersistentEntity<?> entity = null;
+		try {
+			entity = mappingContext.getRequiredPersistentEntity(source.getClass());
+		} catch(InaccessibleObjectException e){
+			try { // punt
+				entity = mappingContext.getRequiredPersistentEntity(Object.class);
+			} catch(Exception ee){
+				throw e;
+			}
+		}
 		PersistentPropertyAccessor<Object> accessor = entity.getPropertyAccessor(source);
 
 		return new ConvertingPropertyAccessor<>(accessor, conversionService);

src/test/java/org/springframework/data/couchbase/core/CouchbaseTemplateQueryIntegrationTests.java

@@ -26,8 +26,12 @@
 import java.time.Instant;
 import java.time.temporal.TemporalAccessor;
 import java.util.Arrays;
+import java.util.HashMap;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Map;
+import java.util.Set;
 import java.util.UUID;
 import java.util.stream.Collectors;
 
@@ -42,6 +46,7 @@
 import org.springframework.data.couchbase.domain.Config;
 import org.springframework.data.couchbase.domain.Course;
 import org.springframework.data.couchbase.domain.NaiveAuditorAware;
+import org.springframework.data.couchbase.domain.PersonWithMaps;
 import org.springframework.data.couchbase.domain.Submission;
 import org.springframework.data.couchbase.domain.User;
 import org.springframework.data.couchbase.domain.UserJustLastName;
@@ -127,6 +132,27 @@ void findByQueryAll() {
 
 	}
 
+
+	@Test
+	void findById() {
+		PersonWithMaps person1 = new PersonWithMaps();
+		person1.setId(UUID.randomUUID().toString());
+		Map<String, Set<String>> versions=new HashMap<>();
+		Set<String> versionSet = new HashSet<>();
+		versionSet.add("1.0");
+		versions.put("v",versionSet);
+		person1.setVersions(versions);
+		Map<String, Map<String, String>> releaseVersions = new HashMap<>();
+		Map<String,String> releaseMap = new HashMap<>();
+		releaseMap.put("1","1");
+		releaseVersions.put("1",releaseMap);
+		person1.setReleaseVersions(releaseVersions);
+		couchbaseTemplate.upsertById(PersonWithMaps.class).one(person1);
+		PersonWithMaps person2 = couchbaseTemplate.findById(PersonWithMaps.class).one(person1.getId());
+	  assertEquals(person1, person2);
+		couchbaseTemplate.removeById(PersonWithMaps.class).oneEntity(person1);
+	}
+
 	@Test
 	void findByMatchingQuery() {
 		User user1 = new User(UUID.randomUUID().toString(), "user1", "user1");

src/test/java/org/springframework/data/couchbase/domain/PersonWithMaps.java

@@ -0,0 +1,29 @@
+package org.springframework.data.couchbase.domain;
+
+import com.couchbase.client.core.deps.com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonInclude;
+import lombok.Data;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.couchbase.core.mapping.Document;
+import org.springframework.data.couchbase.core.mapping.Field;
+
+import java.util.Map;
+import java.util.Set;
+
+@Data
+@JsonIgnoreProperties(ignoreUnknown = true)
+@JsonInclude(JsonInclude.Include.NON_NULL)
+@Document
+public class PersonWithMaps {
+
+  @Id
+  private String id;
+  @Field
+  private Map<String, Set<String>> versions;
+  @Field
+  private Map<String, Map<String,String>> releaseVersions;
+
+  public PersonWithMaps(){
+
+  }
+}