[JENKINS-26107] StepContext.hasBody implementation.

pom.xml

@@ -69,7 +69,7 @@
        <dependency>
            <groupId>${project.groupId}</groupId>
            <artifactId>workflow-step-api</artifactId>
            <version>1.15</version>
            <version>2.1-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>${project.groupId}</groupId>

src/main/java/org/jenkinsci/plugins/workflow/cps/CpsStepContext.java

@@ -152,7 +152,7 @@
     *
     * This is the implicit closure block passed to the step invocation.
     */
    private BodyReference body;
    private @CheckForNull BodyReference body;

    private final int threadId;

@@ -174,12 +174,12 @@
    private transient volatile boolean loadingThreadGroup;

    @CpsVmThreadOnly
    CpsStepContext(StepDescriptor step, CpsThread thread, FlowExecutionOwner executionRef, FlowNode node, Closure body) {
    CpsStepContext(StepDescriptor step, CpsThread thread, FlowExecutionOwner executionRef, FlowNode node, @CheckForNull Closure body) {
        this.threadId = thread.id;
        this.executionRef = executionRef;
        this.id = node.getId();
        this.node = node;
        this.body = thread.group.export(body);
        this.body = body != null ? thread.group.export(body) : null;
        this.stepDescriptorId = step.getId();
    }

@@ -269,14 +269,19 @@ public String getDisplayName() {
        }
    }

    @Override public boolean hasBody() {
        return body != null;
    }

    @Override
    public CpsBodyInvoker newBodyInvoker() {
        if (body == null) {
            throw new IllegalStateException("There is no body to invoke");
        }
        return newBodyInvoker(body);
    }

    public CpsBodyInvoker newBodyInvoker(BodyReference body) {
        if (body==null)
            throw new IllegalStateException("There's no body to invoke");
    public @Nonnull CpsBodyInvoker newBodyInvoker(@Nonnull BodyReference body) {
        return new CpsBodyInvoker(this,body);
    }

src/main/java/org/jenkinsci/plugins/workflow/cps/CpsThreadGroup.java

@@ -60,6 +60,7 @@
import java.util.logging.Logger;

import static java.util.logging.Level.*;
import javax.annotation.Nonnull;
import org.codehaus.mojo.animal_sniffer.IgnoreJRERequirement;
import static org.jenkinsci.plugins.workflow.cps.CpsFlowExecution.*;
import static org.jenkinsci.plugins.workflow.cps.persistence.PersistenceContext.*;
@@ -149,17 +150,15 @@ public CpsThread getThread(int id) {
    }

    @CpsVmThreadOnly("root")
    public BodyReference export(Closure body) {
    public @Nonnull BodyReference export(@Nonnull Closure body) {
        assertVmThread();
        if (body==null)     return null;
        int id = iota++;
        closures.put(id, body);
        return new StaticBodyReference(id,body);
    }

    @CpsVmThreadOnly("root")
    public BodyReference export(final Script body) {
        if (body==null)     return null;
    public @Nonnull BodyReference export(@Nonnull final Script body) {
        return export(new Closure(null) {
            @Override
            public Object call() {