The blobstore type field is editable. If you put in a value that is not in the list and save you get an NPE (see screenshot).
2018-01-11 16:43:34,179-0600 ERROR [qtp1849456833-166] admin org.sonatype.nexus.extdirect.internal.ExtDirectServlet - Failed to invoke action method: coreui_Blobstore.create, java-method: org.sonatype.nexus.coreui.BlobStoreComponent.create java.lang.NullPointerException: null at org.sonatype.nexus.repository.internal.blobstore.BlobStoreManagerImpl.newBlobStore(BlobStoreManagerImpl.java:200) at org.sonatype.nexus.repository.internal.blobstore.BlobStoreManagerImpl.create(BlobStoreManagerImpl.java:150) at org.sonatype.nexus.common.stateguard.MethodInvocationAction.run(MethodInvocationAction.java:39) at org.sonatype.nexus.common.stateguard.StateGuard$GuardImpl.run(StateGuard.java:270) at org.sonatype.nexus.common.stateguard.GuardedInterceptor.invoke(GuardedInterceptor.java:53) at org.sonatype.nexus.blobstore.api.BlobStoreManager$create$0.call(Unknown Source) at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48) at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113) at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:125) at org.sonatype.nexus.coreui.BlobStoreComponent.create(BlobStoreComponent.groovy:88) at com.palominolabs.metrics.guice.ExceptionMeteredInterceptor.invoke(ExceptionMeteredInterceptor.java:49) at com.palominolabs.metrics.guice.TimedInterceptor.invoke(TimedInterceptor.java:47) at org.sonatype.nexus.validation.internal.ValidationInterceptor.invoke(ValidationInterceptor.java:53) at org.apache.shiro.guice.aop.AopAllianceMethodInvocationAdapter.proceed(AopAllianceMethodInvocationAdapter.java:49) at org.apache.shiro.authz.aop.AuthorizingAnnotationMethodInterceptor.invoke(AuthorizingAnnotationMethodInterceptor.java:68) at org.apache.shiro.guice.aop.AopAllianceMethodInterceptorAdapter.invoke(AopAllianceMethodInterceptorAdapter.java:36) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498)