withDockerRegistry([credentialsId: 'gcr:long-disk-191222', url: 'https://gcr.io']) {
 {{ sh "docker push $IMAGE_REPO:$IMAGE_TAG"}}
 }
Error:
 java.lang.NullPointerException
 at org.jenkinsci.plugins.docker.workflow.RegistryEndpointStep$Execution.newKeyMaterialFactory(RegistryEndpointStep.java:81)
 at org.jenkinsci.plugins.docker.workflow.AbstractEndpointStepExecution.start(AbstractEndpointStepExecution.java:44)
 at org.jenkinsci.plugins.workflow.cps.DSL.invokeStep(DSL.java:229)
 at org.jenkinsci.plugins.workflow.cps.DSL.invokeMethod(DSL.java:153)
 at org.jenkinsci.plugins.workflow.cps.CpsScript.invokeMethod(CpsScript.java:122)
 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)
 at org.codehaus.groovy.reflection.CachedMethod.invoke(CachedMethod.java:93)
 at groovy.lang.MetaMethod.doMethodInvoke(MetaMethod.java:325)
 at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1213)
 at groovy.lang.MetaClassImpl.invokeMethod(MetaClassImpl.java:1022)
 at org.codehaus.groovy.runtime.callsite.PogoMetaClassSite.call(PogoMetaClassSite.java:42)
 at org.codehaus.groovy.runtime.callsite.CallSiteArray.defaultCall(CallSiteArray.java:48)
 at org.codehaus.groovy.runtime.callsite.AbstractCallSite.call(AbstractCallSite.java:113)
 at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:157)
 at org.kohsuke.groovy.sandbox.GroovyInterceptor.onMethodCall(GroovyInterceptor.java:23)
 at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SandboxInterceptor.onMethodCall(SandboxInterceptor.java:133)
 at org.kohsuke.groovy.sandbox.impl.Checker$1.call(Checker.java:155)
 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:159)
 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:129)
 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:129)
 at org.kohsuke.groovy.sandbox.impl.Checker.checkedCall(Checker.java:129)
 at com.cloudbees.groovy.cps.sandbox.SandboxInvoker.methodCall(SandboxInvoker.java:17)
 at WorkflowScript.run(WorkflowScript:33)
 at __cps.transform__(Native Method)
 at com.cloudbees.groovy.cps.impl.ContinuationGroup.methodCall(ContinuationGroup.java:57)
 at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.dispatchOrArg(FunctionCallBlock.java:109)
 at com.cloudbees.groovy.cps.impl.FunctionCallBlock$ContinuationImpl.fixArg(FunctionCallBlock.java:82)
 at sun.reflect.GeneratedMethodAccessor230.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
 at java.lang.reflect.Method.invoke(Method.java:498)
 at com.cloudbees.groovy.cps.impl.ContinuationPtr$ContinuationImpl.receive(ContinuationPtr.java:72)
 at com.cloudbees.groovy.cps.impl.ClosureBlock.eval(ClosureBlock.java:46)
 at com.cloudbees.groovy.cps.Next.step(Next.java:83)
 at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:174)
 at com.cloudbees.groovy.cps.Continuable$1.call(Continuable.java:163)
 at org.codehaus.groovy.runtime.GroovyCategorySupport$ThreadCategoryInfo.use(GroovyCategorySupport.java:122)
 at org.codehaus.groovy.runtime.GroovyCategorySupport.use(GroovyCategorySupport.java:261)
 at com.cloudbees.groovy.cps.Continuable.run0(Continuable.java:163)
 at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.access$101(SandboxContinuable.java:34)
 at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.lambda$run0$0(SandboxContinuable.java:59)
 at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.GroovySandbox.runInSandbox(GroovySandbox.java:108)
 at org.jenkinsci.plugins.workflow.cps.SandboxContinuable.run0(SandboxContinuable.java:58)
 at org.jenkinsci.plugins.workflow.cps.CpsThread.runNextChunk(CpsThread.java:174)
 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.run(CpsThreadGroup.java:332)
 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup.access$200(CpsThreadGroup.java:83)
 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:244)
 at org.jenkinsci.plugins.workflow.cps.CpsThreadGroup$2.call(CpsThreadGroup.java:232)
 at org.jenkinsci.plugins.workflow.cps.CpsVmExecutorService$2.call(CpsVmExecutorService.java:64)
 at java.util.concurrent.FutureTask.run(FutureTask.java:266)
 at hudson.remoting.SingleLaneExecutorService$1.run(SingleLaneExecutorService.java:131)
 at jenkins.util.ContextResettingExecutorService$1.run(ContextResettingExecutorService.java:28)
 at jenkins.security.ImpersonatingExecutorService$1.run(ImpersonatingExecutorService.java:59)
 at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
 at java.util.concurrent.FutureTask.run(FutureTask.java:266)
 at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
 at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
 at java.lang.Thread.run(Thread.java:748)
 Finished: FAILURE