NullPointerException when using arrow functions with argument named "argument"

Input for `SIMPLE_OPTIMIZATIONS`:

```
throw ((arguments) => { })
```

Error output:

```
Exception in thread "main" java.lang.RuntimeException: INTERNAL COMPILER ERROR.
Please report this problem.

null
Node(NAME arguments): input:1:8
throw ((arguments) => { })
Parent(PARAM_LIST): input:1:7
throw ((arguments) => { })

at com.google.javascript.jscomp.VarCheck$RedeclarationCheckHandler.onRedeclaration(VarCheck.java:462)
at com.google.javascript.jscomp.Es6SyntacticScopeCreator$ScopeScanner.declareVar(Es6SyntacticScopeCreator.java:330)
at com.google.javascript.jscomp.Es6SyntacticScopeCreator$ScopeScanner.declareLHS(Es6SyntacticScopeCreator.java:191)
at com.google.javascript.jscomp.Es6SyntacticScopeCreator$ScopeScanner.populate(Es6SyntacticScopeCreator.java:134)
at com.google.javascript.jscomp.Es6SyntacticScopeCreator.createScope(Es6SyntacticScopeCreator.java:91)
at com.google.javascript.jscomp.Es6SyntacticScopeCreator.createScope(Es6SyntacticScopeCreator.java:35)
at com.google.javascript.jscomp.NodeTraversal.getAbstractScope(NodeTraversal.java:1065)
at com.google.javascript.jscomp.NodeTraversal.getScope(NodeTraversal.java:1141)
at com.google.javascript.jscomp.VarCheck.visit(VarCheck.java:193)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:867)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:979)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:863)
at com.google.javascript.jscomp.NodeTraversal.traverseFunction(NodeTraversal.java:902)
at com.google.javascript.jscomp.NodeTraversal.handleFunction(NodeTraversal.java:816)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:842)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:979)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:863)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:979)
at com.google.javascript.jscomp.NodeTraversal.handleScript(NodeTraversal.java:804)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:839)
at com.google.javascript.jscomp.NodeTraversal.traverseChildren(NodeTraversal.java:979)
at com.google.javascript.jscomp.NodeTraversal.traverseBranch(NodeTraversal.java:863)
at com.google.javascript.jscomp.NodeTraversal.traverseRoots(NodeTraversal.java:401)
at com.google.javascript.jscomp.VarCheck.process(VarCheck.java:145)
at com.google.javascript.jscomp.PhaseOptimizer$NamedPass.process(PhaseOptimizer.java:328)
at com.google.javascript.jscomp.PhaseOptimizer.process(PhaseOptimizer.java:237)
at com.google.javascript.jscomp.Compiler.check(Compiler.java:1011)
at com.google.javascript.jscomp.Compiler.performChecksAndTranspilation(Compiler.java:819)
at com.google.javascript.jscomp.Compiler.lambda$stage1Passes$0(Compiler.java:749)
at com.google.javascript.jscomp.CompilerExecutor.runInCompilerThread(CompilerExecutor.java:129)
at com.google.javascript.jscomp.Compiler.runInCompilerThread(Compiler.java:807)
at com.google.javascript.jscomp.Compiler.stage1Passes(Compiler.java:747)
at com.google.javascript.jscomp.Compiler.compile(Compiler.java:665)
at com.google.javascript.jscomp.Compiler.compile(Compiler.java:634)
at examples.CompilerTest.main(CompilerTest.java:67)
Caused by: java.lang.NullPointerException
... 35 more
```

Affects: v20190415 and current master (2375110b30ccb83b0a550c8c3d46c526e3896d62)