Resolve Nil Validator Panic (#6218)

* resolve proposer panic
* Merge refs/heads/master into panic-proposer-slashed

beacon-chain/state/getters.go

@@ -75,11 +75,17 @@ func (v *ReadOnlyValidator) WithdrawalCredentials() []byte {
 
 // Slashed returns the read only validator is slashed.
 func (v *ReadOnlyValidator) Slashed() bool {
+	if v == nil || v.validator == nil {
+		return false
+	}
 	return v.validator.Slashed
 }
 
 // CopyValidator returns the copy of the read only validator.
 func (v *ReadOnlyValidator) CopyValidator() *ethpb.Validator {
+	if v == nil || v.validator == nil {
+		return nil
+	}
 	return CopyValidator(v.validator)
 }
 

beacon-chain/state/getters_test.go

@@ -75,3 +75,13 @@ func TestNilState_NoPanic(t *testing.T) {
 	_ = st.FinalizedCheckpoint()
 	_ = err
 }
+
+func TestReadOnlyValidator_NoPanic(t *testing.T) {
+	v := &ReadOnlyValidator{}
+	if v.Slashed() == true {
+		t.Error("Expected not slashed")
+	}
+	if v.CopyValidator() != nil {
+		t.Error("Expected nil result")
+	}
+}