Typing (pressing) = (equal sign character) on 4th method edit line brings a debugger

[patrik.svestka@…]

I wanted to delete some text. So I took it to block deleted it via backspace. Then I deleted some variables (by selection and backspace). Then I moved the cursor below it at the start of the line and tried to type =, got a debugger window with [SubscriptOutOfBoundsError]: subscript (0) out of bounds in process NewSystemBrowser [171] instead. Other characters work. When I deleted the whole line and pressed return, I could then type the = character.

Here is the walkback text:

[SubscriptOutOfBoundsError]: subscript (0) out of bounds in process NewSystemBrowser [171]

String(Object) >> subscriptBoundsError: 0 {1409024} [11]
String(Object) >> indexNotIntegerOrOutOfBounds: 0 {1413120} [11]
String(Object) >> basicAt: 0 {1417216} [281]
String >> basicAt: 0 {1421312} [36]
String >> at: 0 {1425408} [35]
SmallSense::SmalltalkEditSupport >> keyPressEqual  {1429504} [10]
SmallSense::SmalltalkEditSupport >> keyPress:x:y:in: $= "16r3D 61" -1 -1 a Tools::CodeView2::TextView {1433600} [61]
SmallSense::EditService >> keyPress:x:y:in: $= "16r3D 61" -1 -1 a Tools::CodeView2::TextView {1437696} [8]
[] in Tools::CodeView2>>keyPress:x:y:in: >> value: a SmallSense::EditService {1441792} [11]
[] in Collection>>contains: >> value: a SmallSense::EditService {1445888} [8]
Array >> from:to:do: 1 7 [] in Collection>>contains: {1449984} [7]
OrderedCollection >> do: [] in Collection>>contains: {1454080} [4]
OrderedCollection(Collection) >> contains: [] in Tools::CodeView2>>keyPress:x:y:in: {1458176} [7]
Tools::CodeView2 >> keyPress:x:y:in: $= "16r3D 61" -1 -1 a Tools::CodeView2::TextView {1462272} [7]
Tools::CodeView2::TextView >> keyPress:x:y: $= "16r3D 61" -1 -1 {1466368} [2]
Tools::CodeView2::TextView(Object) >> perform:withArguments: #keyPress:x:y: #($= "16r3D 61" -1 -1) {1470464} [170]
Tools::CodeView2::TextView(DisplaySurface) >> dispatchEvent:type:arguments:withFocusOn:delegate: WindowEvent::KeyPressEvent(#keyPress:x:y: view: ApplicationWindow args: #($= "16r3D 61" -1 -1)) #keyPress:x:y: #($= "16r3D 61" -1 -1) nil true {1474560} [238]
Tools::CodeView2::TextView(DisplaySurface) >> dispatchEvent:withFocusOn:delegate: WindowEvent::KeyPressEvent(#keyPress:x:y: view: ApplicationWindow args: #($= "16r3D 61" -1 -1)) nil true {1478656} [5]
ApplicationWindow(DisplaySurface) >> dispatchEvent:type:arguments:withFocusOn:delegate: WindowEvent::KeyPressEvent(#keyPress:x:y: view: ApplicationWindow args: #($= "16r3D 61" 396 393)) #keyPress:x:y: #($= "16r3D 61" 396 393) a Tools::CodeView2::TextView true {1482752} [140]
ApplicationWindow(DisplaySurface) >> dispatchEvent:withFocusOn:delegate: WindowEvent::KeyPressEvent(#keyPress:x:y: view: ApplicationWindow args: #($= "16r3D 61" 396 393)) a Tools::CodeView2::TextView true {1486848} [5]
[] in WindowGroup>>processEventsWithModalGroup: >> value  {1490944} [221]
Block >> on:do:ensure: LastEventQuery (private in WindowGroup) [] in WindowGroup>>processEventsWithModalGroup: [] in WindowGroup>>processEventsWithModalGroup: {1495040} [15]
WindowGroup >> processEventsWithModalGroup: nil {1499136} [232]
[] in WindowGroup>>eventLoopWhile:onLeave: >> value  {1503232} [152]
SignalSet >> handle:do: [] in WindowGroup>>eventLoopWhile:onLeave: [] in WindowGroup>>eventLoopWhile:onLeave: {1507328} [14]
[] in WindowGroup>>eventLoopWhile:onLeave: >> value  {1511424} [81]
Block >> ensure: [] in WindowGroup>>startupWith: (optimized) {1515520} [12]
[] in WindowGroup>>eventLoopWhile:onLeave: >> value {1519616} [184]
WindowGroup::WindowGroupQuery class(Notification class) >> answer:do: WindowGroup(NewSystemBrowser) [] in WindowGroup>>eventLoopWhile:onLeave: {1523712} [10]
[] in WindowGroup::WindowGroupQuery class>>answer:do: >> value {1527808} [4]
Block >> ensure: [] in WindowGroup::WindowGroupQuery class>>answer:do: (optimized) {1531904} [12]
WindowGroup::WindowGroupQuery class >> answer:do: WindowGroup(NewSystemBrowser) [] in WindowGroup>>eventLoopWhile:onLeave: {1536000} [5]
WindowGroup >> eventLoopWhile:onLeave: [] in WindowGroup>>startupWith: (optimized) [] in WindowGroup>>startupWith: (optimized) {1540096} [25]
[] in WindowGroup>>startupWith: >> value {1544192} [26]
Block >> ensure: [] in WindowGroup>>startupWith: {1548288} [12]
[] in WindowGroup>>startupWith: >> value  {1552384} [27]
ExceptionHandlerSet >> handleDo: [] in WindowGroup>>startupWith: {1556480} [14]
[] in Process>>start >> value {1560576} [34]
Block >> on:do:ensure: SignalSet(RestartProcessRequest AbortAllOperationRequest TerminateProcessRequest) [] in Process>>start [] in Process>>start {1564672} [15]
Process >> start  {1568768} [35]
UndefinedObject >> nil  {1572864} [0]