diff --git a/de.metas.business.rest-api-impl/src/main/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonPersisterService.java b/de.metas.business.rest-api-impl/src/main/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonPersisterService.java
index 66df92d5805..11508206426 100644
--- a/de.metas.business.rest-api-impl/src/main/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonPersisterService.java
+++ b/de.metas.business.rest-api-impl/src/main/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonPersisterService.java
@@ -312,7 +312,10 @@ public BPartnerComposite persist(
 		{
 			if (effectiveSyncAdvise.isFailIfNotExists())
 			{
-				throw new MissingResourceException("bpartner");
+				throw new MissingResourceException(
+						"Did not find an existing partner with identifier '" + bpartnerIdentifierStr + "'",
+						jsonBPartnerComposite)
+								.setParameter("effectiveSyncAdvise", effectiveSyncAdvise);
 			}
 			// create new aggregation root
 			bpartnerComposite = BPartnerComposite.builder().build();
@@ -347,7 +350,9 @@ public BPartnerContact persist(
 		{
 			if (parentSyncAdvise.isFailIfNotExists())
 			{
-				throw new MissingResourceException("jsonContact");
+				throw new MissingResourceException(
+						"Did not find an existing contact with identifier '" + contactIdentifierStr + "'")
+								.setParameter("effectiveSyncAdvise", parentSyncAdvise);
 			}
 			if (jsonContact.getMetasfreshBPartnerId() == null)
 			{
diff --git a/de.metas.business.rest-api-impl/src/test/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonRetrieverServiceTest.java b/de.metas.business.rest-api-impl/src/test/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonRetrieverServiceTest.java
index 81e0dc65995..bbffa295dbe 100644
--- a/de.metas.business.rest-api-impl/src/test/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonRetrieverServiceTest.java
+++ b/de.metas.business.rest-api-impl/src/test/java/de/metas/rest_api/bpartner/impl/bpartnercomposite/JsonRetrieverServiceTest.java
@@ -74,7 +74,8 @@ void init()
 	{
 		AdempiereTestHelper.get().init();
 
-		BPartnerCompositeRepository bpartnerCompositeRepository = new BPartnerCompositeRepository(new MockLogEntriesRepository());
+		final BPartnerCompositeRepository bpartnerCompositeRepository = new BPartnerCompositeRepository(new MockLogEntriesRepository());
+
 		final JsonServiceFactory jsonServiceFactory = new JsonServiceFactory(
 				bpartnerCompositeRepository,
 				new BPGroupRepository(),
diff --git a/de.metas.business.rest-api/src/main/java/de/metas/rest_api/bpartner/response/JsonResponseBPartner.java b/de.metas.business.rest-api/src/main/java/de/metas/rest_api/bpartner/response/JsonResponseBPartner.java
index 2541f37f28c..c4939d4b2ae 100644
--- a/de.metas.business.rest-api/src/main/java/de/metas/rest_api/bpartner/response/JsonResponseBPartner.java
+++ b/de.metas.business.rest-api/src/main/java/de/metas/rest_api/bpartner/response/JsonResponseBPartner.java
@@ -66,45 +66,45 @@ public class JsonResponseBPartner
 	MetasfreshId metasfreshId;
 
 	@ApiModelProperty( //
-			allowEmptyValue = true, //
+			required = false, //
 			dataType = "java.lang.String", //
 			value = "This translates to `C_BPartner.ExternalId`.")
 	@JsonInclude(Include.NON_NULL)
 	JsonExternalId externalId;
 
-	@ApiModelProperty(allowEmptyValue = false, value = "This translates to `C_BPartner.Value`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.Value`.")
 	String code;
 
-	@ApiModelProperty(allowEmptyValue = false, value = "This translates to `C_BPartner.IsActive`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.IsActive`.")
 	boolean active;
 
-	@ApiModelProperty(allowEmptyValue = false, value = "This translates to `C_BPartner.Name`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.Name`.")
 	String name;
 
-	@ApiModelProperty(allowEmptyValue = true, value = "This translates to `C_BPartner.Name2`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.Name2`.")
 	@JsonInclude(Include.NON_NULL)
 	String name2;
 
-	@ApiModelProperty(allowEmptyValue = true, value = "This translates to `C_BPartner.Name3`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.Name3`.")
 	@JsonInclude(Include.NON_NULL)
 	String name3;
 
 	@ApiModelProperty( //
-			allowEmptyValue = true, //
+			required = false, //
 			value = "This translates to `C_BPartner.CompanyName`.\n"
 					+ "If set, the the respective `C_BPartner` record will also have `IsCompany='Y'`")
 	@JsonInclude(Include.NON_NULL)
 	String companyName;
 
 	@ApiModelProperty( //
-			allowEmptyValue = true, //
+			required = false, //
 			value = "This translates to `C_BPartner.BPartner_Parent_ID`. It's a this bpartner's central/parent company",//
 			dataType = "java.lang.Integer")
 	@JsonInclude(Include.NON_NULL)
 	MetasfreshId parentId;
 
 	@ApiModelProperty( //
-			allowEmptyValue = true, //
+			required = false, //
 			value = "This translates to `C_BPartner.Phone2`. It's this bpartner's central phone number")
 	@JsonInclude(Include.NON_NULL)
 	String phone;
@@ -112,20 +112,20 @@ public class JsonResponseBPartner
 	@JsonInclude(Include.NON_NULL)
 	String language;
 
-	@ApiModelProperty(allowEmptyValue = true, value = "This translates to `C_BPartner.URL`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.URL`.")
 	@JsonInclude(Include.NON_NULL)
 	String url;
 
-	@ApiModelProperty(allowEmptyValue = true, value = "This translates to `C_BPartner.URL2`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.URL2`.")
 	@JsonInclude(Include.NON_NULL)
 	private String url2;
 
-	@ApiModelProperty(allowEmptyValue = true, value = "This translates to `C_BPartner.URL3`.")
+	@ApiModelProperty(required = false, value = "This translates to `C_BPartner.URL3`.")
 	@JsonInclude(Include.NON_NULL)
 	private String url3;
 
 	@ApiModelProperty( //
-			allowEmptyValue = true, //
+			required = false, //
 			value = "Name of the business partner's group")
 	@JsonInclude(Include.NON_NULL)
 	String group;
@@ -138,7 +138,7 @@ public class JsonResponseBPartner
 	@Builder(toBuilder = true)
 	private JsonResponseBPartner(
 			@JsonProperty(METASFRESH_ID) @NonNull final MetasfreshId metasfreshId,
-			@JsonProperty(EXTERNAL_ID) @NonNull final JsonExternalId externalId,
+			@JsonProperty(EXTERNAL_ID) @Nullable final JsonExternalId externalId,
 			@JsonProperty(CODE) @NonNull final String code,
 			@JsonProperty(ACTIVE) @NonNull final Boolean active,
 			@JsonProperty(NAME) @NonNull final String name,