Add nil checks for type values when processing objects

[pwschuurman]

Ran into the below two nil-ptr exceptions.

Culprit seemed to be due to parsing a runtime.itabTableType resource:

 2 40960 81920 [1+8?]runtime.itabTableType 

Added two nil-ptr checks to skip if a nil type is encountered.

Core "tmp/core.283046" was generated by "/gce-pd-csi-driver" Entering interactive mode (type 'help' for commands) (viewcore) histogram Error while trying to run command "histogram": runtime error: invalid memory address or nil pointer dereference Stack: goroutine 1 [running]: runtime/debug.Stack() /usr/lib/google-golang/src/runtime/debug/stack.go:26 +0x5e main.capturePanic.func1() /workspace/debug/cmd/viewcore/main.go:372 +0x3d panic({0x9e8b20?, 0xecb700?}) /usr/lib/google-golang/src/runtime/panic.go:799 +0x132 golang.org/x/debug/internal/gocore.(*Type).field(...) /workspace/debug/internal/gocore/type.go:86 golang.org/x/debug/internal/gocore.runtimeItab.Type(...) /workspace/debug/internal/gocore/type.go:196 golang.org/x/debug/internal/gocore.(*Process).typeObject(0xc000280000, 0x300b8f0, 0xc001f242a0, {0xb348b0, 0xc000274000}, 0xc00b1e3280) /workspace/debug/internal/gocore/type.go:645 +0x155 golang.org/x/debug/internal/gocore.(*Process).doTypeHeap.func2(0x0?) /workspace/debug/internal/gocore/type.go:536 +0x91 golang.org/x/debug/internal/gocore.(*Process).ForEachRoot(...) /workspace/debug/internal/gocore/object.go:191 golang.org/x/debug/internal/gocore.(*Process).doTypeHeap(0xc000280000) /workspace/debug/internal/gocore/type.go:529 +0x1f6 sync.(*Once).doSlow(0x564562?, 0xc00b1e3560?) /usr/lib/google-golang/src/sync/once.go:78 +0xab sync.(*Once).Do(...) /usr/lib/google-golang/src/sync/once.go:69 golang.org/x/debug/internal/gocore.(*Process).typeHeap(...) /workspace/debug/internal/gocore/type.go:400 golang.org/x/debug/internal/gocore.(*Process).Type(0xc000280000, 0xc000034000) /workspace/debug/internal/gocore/object.go:219 +0x4a main.typeName(0xc000280000, 0xc000034000) /workspace/debug/cmd/viewcore/main.go:789 +0x9e main.runHistogram.func1(0xc000280000?, 0xc000034000, 0x8?) /workspace/debug/cmd/viewcore/main.go:484 +0x3a golang.org/x/debug/internal/gocore.(*Process).ForEachRootPtr.func1(0x0, 0xc00b35afc0?) /workspace/debug/internal/gocore/object.go:257 +0x3f golang.org/x/debug/internal/gocore.walkRootTypePtrs(0xc000280000, 0xc002b15bc0, {0xc00b1e3718, 0x8, 0x8}, 0x0, 0xc007c4c360?, 0xc00b1e3720) /workspace/debug/internal/gocore/root.go:163 +0x2ab golang.org/x/debug/internal/gocore.(*Process).forEachRootPtr(...) /workspace/debug/internal/gocore/object.go:269 golang.org/x/debug/internal/gocore.(*Process).ForEachRootPtr(0xc0000fa300?, 0xa6acf5?, 0x3?) /workspace/debug/internal/gocore/object.go:254 +0x4b main.runHistogram(0xc0000fa300?, {0xeffd80?, 0x4?, 0xa6b4df?}) /workspace/debug/cmd/viewcore/main.go:483 +0x1fb github.com/spf13/cobra.(*Command).execute(0xed62e0, {0xeffd80, 0x0, 0x0}) /gopath/go/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:944 +0x843 github.com/spf13/cobra.(*Command).ExecuteC(0xc0000ff208) /gopath/go/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:1068 +0x3a5 github.com/spf13/cobra.(*Command).Execute(...) /gopath/go/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:992 main.runRoot.func2() /workspace/debug/cmd/viewcore/main.go:361 +0x7c main.capturePanic(0xb32820?) /workspace/debug/cmd/viewcore/main.go:376 +0x51 main.runRoot(0xed5760, {0xc00007e880?, 0x4?, 0xa6b4df?}) /workspace/debug/cmd/viewcore/main.go:358 +0x672 github.com/spf13/cobra.(*Command).execute(0xed5760, {0xc000022120, 0x2, 0x2}) /gopath/go/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:944 +0x843 github.com/spf13/cobra.(*Command).ExecuteC(0xed5760) /gopath/go/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:1068 +0x3a5 github.com/spf13/cobra.(*Command).Execute(...) /gopath/go/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:992 main.main() /workspace/debug/cmd/viewcore/main.go:244 +0x132 

Core "tmp/core.283046" was generated by "/gce-pd-csi-driver" Entering interactive mode (type 'help' for commands) (viewcore) histogram Error while trying to run command "histogram": runtime error: invalid memory address or nil pointer dereference Stack: goroutine 1 [running]: runtime/debug.Stack() /usr/lib/google-golang/src/runtime/debug/stack.go:26 +0x5e main.capturePanic.func1() /workspace/debug/cmd/viewcore/main.go:372 +0x3d panic({0x9e8b20?, 0xecb700?}) /usr/lib/google-golang/src/runtime/panic.go:799 +0x132 golang.org/x/debug/internal/gocore.(*Process).typeObject(0xc0002ca000, 0x300b8f0, 0xc0033a8300, {0xb348b0, 0xc0002be000}, 0xc00b28d280) /workspace/debug/internal/gocore/type.go:648 +0xedb golang.org/x/debug/internal/gocore.(*Process).doTypeHeap.func2(0x0?) /workspace/debug/internal/gocore/type.go:539 +0x91 golang.org/x/debug/internal/gocore.(*Process).ForEachRoot(...) /workspace/debug/internal/gocore/object.go:191 golang.org/x/debug/internal/gocore.(*Process).doTypeHeap(0xc0002ca000) /workspace/debug/internal/gocore/type.go:532 +0x1f6 sync.(*Once).doSlow(0x564562?, 0xc00b28d560?) /usr/lib/google-golang/src/sync/once.go:78 +0xab sync.(*Once).Do(...) /usr/lib/google-golang/src/sync/once.go:69 golang.org/x/debug/internal/gocore.(*Process).typeHeap(...) /workspace/debug/internal/gocore/type.go:403 golang.org/x/debug/internal/gocore.(*Process).Type(0xc0002ca000, 0xc000034000) /workspace/debug/internal/gocore/object.go:219 +0x4a main.typeName(0xc0002ca000, 0xc000034000) /workspace/debug/cmd/viewcore/main.go:789 +0x9e main.runHistogram.func1(0xc0002ca000?, 0xc000034000, 0x8?) /workspace/debug/cmd/viewcore/main.go:484 +0x3a golang.org/x/debug/internal/gocore.(*Process).ForEachRootPtr.func1(0x0, 0xc00ac7f440?) /workspace/debug/internal/gocore/object.go:257 +0x3f golang.org/x/debug/internal/gocore.walkRootTypePtrs(0xc0002ca000, 0xc007396480, {0xc00b28d718, 0x8, 0x8}, 0x0, 0xc00826cea0?, 0xc00b28d720) /workspace/debug/internal/gocore/root.go:163 +0x2ab golang.org/x/debug/internal/gocore.(*Process).forEachRootPtr(...) /workspace/debug/internal/gocore/object.go:269 golang.org/x/debug/internal/gocore.(*Process).ForEachRootPtr(0xc00017e300?, 0xa6acf5?, 0x3?) /workspace/debug/internal/gocore/object.go:254 +0x4b main.runHistogram(0xc00017e300?, {0xeffd80?, 0x4?, 0xa6b4df?}) /workspace/debug/cmd/viewcore/main.go:483 +0x1fb github.com/spf13/cobra.(*Command).execute(0xed62e0, {0xeffd80, 0x0, 0x0}) /gopath/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:944 +0x843 github.com/spf13/cobra.(*Command).ExecuteC(0xc000187208) /gopath/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:1068 +0x3a5 github.com/spf13/cobra.(*Command).Execute(...) /gopath/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:992 main.runRoot.func2() /workspace/debug/cmd/viewcore/main.go:361 +0x7c main.capturePanic(0xb32820?) /workspace/debug/cmd/viewcore/main.go:376 +0x51 main.runRoot(0xed5760, {0xc00012a860?, 0x4?, 0xa6b4df?}) /workspace/debug/cmd/viewcore/main.go:358 +0x672 github.com/spf13/cobra.(*Command).execute(0xed5760, {0xc0001300a0, 0x2, 0x2}) /gopath/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:944 +0x843 github.com/spf13/cobra.(*Command).ExecuteC(0xed5760) /gopath/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:1068 +0x3a5 github.com/spf13/cobra.(*Command).Execute(...) /gopath/pkg/mod/github.com/spf13/cobra@v1.7.0/command.go:992 main.main() /workspace/debug/cmd/viewcore/main.go:244 +0x132 

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