String a;
a = "abc";

FATAL: BUG! exception in phase 'class generation' in source unit 'Script1.groovy' Error while popping argument from operand stack tracker in class Script1 method java.lang.Object run().
BUG! exception in phase 'class generation' in source unit 'Script1.groovy' Error while popping argument from operand stack tracker in class Script1 method java.lang.Object run().
	at org.codehaus.groovy.classgen.asm.OperandStack.popWithMessage(OperandStack.java:72)
	at org.codehaus.groovy.classgen.asm.OperandStack.remove(OperandStack.java:207)
	at org.codehaus.groovy.classgen.asm.OperandStack.replace(OperandStack.java:274)
	at org.codehaus.groovy.classgen.asm.CallSiteWriter.makeCallSite(CallSiteWriter.java:336)
	at org.codehaus.groovy.classgen.asm.InvocationWriter.makeCachedCall(InvocationWriter.java:307)
	at org.codehaus.groovy.classgen.asm.InvocationWriter.makeCall(InvocationWriter.java:397)
	at org.codehaus.groovy.classgen.asm.InvocationWriter.makeCall(InvocationWriter.java:104)
	at org.codehaus.groovy.classgen.asm.InvocationWriter.writeInvokeStaticMethod(InvocationWriter.java:515)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitStaticMethodCallExpression(AsmClassGenerator.java:807)
	at org.codehaus.groovy.ast.expr.StaticMethodCallExpression.visit(StaticMethodCallExpression.java:46)
	at org.codehaus.groovy.classgen.asm.BinaryExpressionHelper.evaluateEqual(BinaryExpressionHelper.java:316)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitDeclarationExpression(AsmClassGenerator.java:637)
	at org.codehaus.groovy.ast.expr.DeclarationExpression.visit(DeclarationExpression.java:89)
	at org.codehaus.groovy.classgen.asm.StatementWriter.writeExpressionStatement(StatementWriter.java:613)
	at org.codehaus.groovy.classgen.asm.OptimizingStatementWriter.writeExpressionStatement(OptimizingStatementWriter.java:366)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitExpressionStatement(AsmClassGenerator.java:624)
	at org.codehaus.groovy.ast.stmt.ExpressionStatement.visit(ExpressionStatement.java:42)
	at org.codehaus.groovy.classgen.asm.StatementWriter.writeBlockStatement(StatementWriter.java:85)
	at org.codehaus.groovy.classgen.asm.OptimizingStatementWriter.writeBlockStatement(OptimizingStatementWriter.java:159)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitBlockStatement(AsmClassGenerator.java:570)
	at org.codehaus.groovy.ast.stmt.BlockStatement.visit(BlockStatement.java:71)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClassCodeContainer(ClassCodeVisitorSupport.java:104)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitConstructorOrMethod(ClassCodeVisitorSupport.java:115)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitStdMethod(AsmClassGenerator.java:434)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitConstructorOrMethod(AsmClassGenerator.java:387)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitMethod(ClassCodeVisitorSupport.java:126)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitMethod(AsmClassGenerator.java:511)
	at org.codehaus.groovy.ast.ClassNode.visitContents(ClassNode.java:1081)
	at org.codehaus.groovy.ast.ClassCodeVisitorSupport.visitClass(ClassCodeVisitorSupport.java:53)
	at org.codehaus.groovy.classgen.AsmClassGenerator.visitClass(AsmClassGenerator.java:233)
	at org.codehaus.groovy.control.CompilationUnit$17.call(CompilationUnit.java:825)
	at org.codehaus.groovy.control.CompilationUnit.applyToPrimaryClassNodes(CompilationUnit.java:1065)
	at org.codehaus.groovy.control.CompilationUnit.doPhaseOperation(CompilationUnit.java:603)
	at org.codehaus.groovy.control.CompilationUnit.processPhaseOperations(CompilationUnit.java:581)
	at org.codehaus.groovy.control.CompilationUnit.compile(CompilationUnit.java:558)
	at groovy.lang.GroovyClassLoader.doParseClass(GroovyClassLoader.java:298)
	at groovy.lang.GroovyClassLoader.parseClass(GroovyClassLoader.java:268)
	at groovy.lang.GroovyShell.parseClass(GroovyShell.java:688)
	at groovy.lang.GroovyShell.parse(GroovyShell.java:700)
	at groovy.lang.GroovyShell.parse(GroovyShell.java:736)
	at groovy.lang.GroovyShell.parse(GroovyShell.java:727)
	at org.jenkinsci.plugins.scriptsecurity.sandbox.groovy.SecureGroovyScript.evaluate(SecureGroovyScript.java:165)
	at hudson.plugins.groovy.SystemGroovy.run(SystemGroovy.java:95)
	at hudson.plugins.groovy.SystemGroovy.perform(SystemGroovy.java:59)
	at hudson.tasks.BuildStepMonitor$1.perform(BuildStepMonitor.java:20)
	at hudson.model.AbstractBuild$AbstractBuildExecution.perform(AbstractBuild.java:730)
	at hudson.model.Build$BuildExecution.build(Build.java:206)
	at hudson.model.Build$BuildExecution.doRun(Build.java:163)
	at hudson.model.AbstractBuild$AbstractBuildExecution.run(AbstractBuild.java:490)
	at hudson.model.Run.execute(Run.java:1737)
	at hudson.model.FreeStyleBuild.run(FreeStyleBuild.java:43)
	at hudson.model.ResourceController.execute(ResourceController.java:97)
	at hudson.model.Executor.run(Executor.java:419)

String a = "";
a = "abc";