[Bug]: Compiler crash in worker when on fail clause is present and a worker returns error

[poorna2152]

Description

Consider the following code,

import ballerina/io;

public function main() returns error? {
    boolean condition = true;
    worker w1 returns error? {
        if condition {
            return error("Error in worker 1");
        }
        0 -> w2;
    }

    worker w2 returns error? {
        int x = check <- w1;
    } on fail {
    }

    error? e = wait w2;

    io:println(e);
}

This code gives a compiler crash,

Resolving Maven dependencies
        Downloading dependencies into /Users/poorna/Documents/issues/lang/xmlns_def/target/platform-libs

Compiling source
        poorna/xmlns_def:0.1.0
ballerina: Oh no, something really went wrong. Bad. Sad.

We appreciate it if you can report the code that broke Ballerina in
https://github.com/ballerina-platform/ballerina-lang/issues with the
log you get below and your sample code.

We thank you for helping make us better.

[2024-04-08 14:03:50,878] SEVERE {b7a.log.crash} - Cannot read field "number" because "targetBB" is null 
java.lang.NullPointerException: Cannot read field "number" because "targetBB" is null
        at org.wso2.ballerinalang.compiler.bir.optimizer.BIRBasicBlockOptimizer.getRemovableBasicBlocks(BIRBasicBlockOptimizer.java:125)
        at org.wso2.ballerinalang.compiler.bir.optimizer.BIRBasicBlockOptimizer.visit(BIRBasicBlockOptimizer.java:79)
        at org.wso2.ballerinalang.compiler.bir.model.BIRNode$BIRFunction.accept(BIRNode.java:432)
        at org.wso2.ballerinalang.compiler.bir.optimizer.BIRBasicBlockOptimizer.lambda$visit$1(BIRBasicBlockOptimizer.java:62)
        at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
        at org.wso2.ballerinalang.compiler.bir.optimizer.BIRBasicBlockOptimizer.visit(BIRBasicBlockOptimizer.java:62)
        at org.wso2.ballerinalang.compiler.bir.model.BIRNode$BIRPackage.accept(BIRNode.java:89)
        at org.wso2.ballerinalang.compiler.bir.optimizer.BIRBasicBlockOptimizer.optimizeNode(BIRBasicBlockOptimizer.java:51)
        at org.wso2.ballerinalang.compiler.bir.optimizer.BIROptimizer.optimizePackage(BIROptimizer.java:99)
        at org.wso2.ballerinalang.compiler.bir.BIRGen.genBIR(BIRGen.java:294)
        at io.ballerina.projects.internal.CompilerPhaseRunner.birGen(CompilerPhaseRunner.java:216)
        at io.ballerina.projects.internal.CompilerPhaseRunner.performBirGenPhases(CompilerPhaseRunner.java:153)
        at io.ballerina.projects.ModuleContext.generateCodeInternal(ModuleContext.java:454)
        at io.ballerina.projects.ModuleCompilationState$4.generatePlatformSpecificCode(ModuleCompilationState.java:132)
        at io.ballerina.projects.ModuleContext.generatePlatformSpecificCode(ModuleContext.java:387)
        at io.ballerina.projects.JBallerinaBackend.performCodeGen(JBallerinaBackend.java:173)
        at io.ballerina.projects.JBallerinaBackend.<init>(JBallerinaBackend.java:142)
        at io.ballerina.projects.JBallerinaBackend.lambda$from$0(JBallerinaBackend.java:126)
        at java.base/java.util.HashMap.computeIfAbsent(HashMap.java:1220)
        at io.ballerina.projects.PackageCompilation.getCompilerBackend(PackageCompilation.java:178)
        at io.ballerina.projects.JBallerinaBackend.from(JBallerinaBackend.java:125)
        at io.ballerina.projects.JBallerinaBackend.from(JBallerinaBackend.java:113)
        at io.ballerina.cli.task.CompileTask.execute(CompileTask.java:216)
        at io.ballerina.cli.TaskExecutor.executeTasks(TaskExecutor.java:40)
        at io.ballerina.cli.cmd.RunCommand.execute(RunCommand.java:254)
        at java.base/java.util.Optional.ifPresent(Optional.java:178)
        at io.ballerina.cli.launcher.Main.main(Main.java:58)
 
WARNING [main.bal:(441:9,441:29)] unused variable 'x'
ERROR [xmlns_def:(1:1,1:1)] Compilation failed due to: Cannot read field "number" because "targetBB" is null
error: compilation contains errors

[gabilang]

The following works without crash,

public function main() returns error? {
    boolean condition = true;
    worker w1 returns error? {
        if condition {
            return error("Error in worker 1");
        } 
        0 -> w2;
    }

    worker w2 returns error? {
        _ = check foo();
        _ = check <- w1;
    } on fail {
        return error("Error in worker 2");
    }

    check wait w2;
}

function foo() returns int|error {
    return 10;
}

It seems the issue happens, when there are check expr only from worker receive actions.