Add null pointer check in G601

fixes: #475

analyzer_test.go

@@ -215,7 +215,7 @@ var _ = Describe("Analyzer", func() {
 		})
 
 		It("should pass the build tags", func() {
-			sample := testutils.SampleCode601[0]
+			sample := testutils.SampleCodeBuildTag[0]
 			source := sample.Code[0]
 			analyzer.LoadRules(rules.Generate().Builders())
 			pkg := testutils.NewTestPackage()

rules/implicit_aliasing.go

@@ -2,9 +2,10 @@ package rules
 
 import (
 	"fmt"
-	"github.com/securego/gosec/v2"
 	"go/ast"
 	"go/token"
+
+	"github.com/securego/gosec/v2"
 )
 
 type implicitAliasing struct {
@@ -33,6 +34,7 @@ func (r *implicitAliasing) Match(n ast.Node, c *gosec.Context) (*gosec.Issue, er
 		// When presented with a range statement, get the underlying Object bound to
 		// by assignment and add it to our set (r.aliases) of objects to check for.
 		if key, ok := node.Value.(*ast.Ident); ok {
+			if key.Obj != nil {
 				if assignment, ok := key.Obj.Decl.(*ast.AssignStmt); ok {
 					if len(assignment.Lhs) < 2 {
 						return nil, nil
@@ -47,6 +49,8 @@ func (r *implicitAliasing) Match(n ast.Node, c *gosec.Context) (*gosec.Issue, er
 					}
 				}
 			}
+		}
+
 	case *ast.UnaryExpr:
 		// If this unary expression is outside of the last range statement we were looking at
 		// then clear the list of objects we're concerned about because they're no longer in

testutils/source.go

@@ -1849,13 +1849,14 @@ func main() {
 	}
 }`}, 1, gosec.NewConfig()}}
 
-	// SampleCodeG601 - Implicit ForRange aliasing
-	SampleCodeG601 = []CodeSample{{[]string{`package main
+	// SampleCodeG601 - Implicit aliasing over range statement
+	SampleCodeG601 = []CodeSample{
+		{[]string{`
+package main
 
 import "fmt"
 
 var vector []*string
-
 func appendVector(s *string) {
 	vector = append(vector, s)
 }
@@ -1882,12 +1883,26 @@ func main() {
 
 	zero, c_star, c := foo()
 	fmt.Printf("%d %v %s", zero, c_start, c)
-}`}, 1, gosec.NewConfig()}}
+}`,
+		}, 1, gosec.NewConfig()},
+		{[]string{`
+// see: github.com/securego/gosec/issues/475
+package main
+import (
+    "fmt"
+)
+func main() {
+    sampleMap := map[string]string{}
+    sampleString := "A string"
+    for sampleString, _ = range sampleMap {
+        fmt.Println(sampleString)
+    }
+}`}, 0, gosec.NewConfig()},
+	}
 
-	// SampleCode601 - Go build tags
-	SampleCode601 = []CodeSample{{[]string{`
+	// SampleCodeBuildTag - G601 build tags
+	SampleCodeBuildTag = []CodeSample{{[]string{`
 // +build tag
-
 package main
 func main() {
   fmt.Println("no package imported error")