diff --git a/core/deserialization/src/org/jetbrains/kotlin/serialization/Flags.java b/core/deserialization/src/org/jetbrains/kotlin/serialization/Flags.java
index 37fec0ade8c..1cba157e892 100644
--- a/core/deserialization/src/org/jetbrains/kotlin/serialization/Flags.java
+++ b/core/deserialization/src/org/jetbrains/kotlin/serialization/Flags.java
@@ -18,6 +18,7 @@ package org.jetbrains.kotlin.serialization;
 
 import com.google.protobuf.Internal;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 import org.jetbrains.kotlin.descriptors.*;
 
 public class Flags {
@@ -25,49 +26,49 @@ public class Flags {
 
     // Common
 
-    public static final FlagField<Boolean> HAS_ANNOTATIONS = FlagField.booleanFirst();
+    public static final BooleanFlagField HAS_ANNOTATIONS = FlagField.booleanFirst();
     public static final FlagField<ProtoBuf.Visibility> VISIBILITY = FlagField.after(HAS_ANNOTATIONS, ProtoBuf.Visibility.values());
     public static final FlagField<ProtoBuf.Modality> MODALITY = FlagField.after(VISIBILITY, ProtoBuf.Modality.values());
 
     // Class
 
     public static final FlagField<ProtoBuf.Class.Kind> CLASS_KIND = FlagField.after(MODALITY, ProtoBuf.Class.Kind.values());
-    public static final FlagField<Boolean> IS_INNER = FlagField.booleanAfter(CLASS_KIND);
+    public static final BooleanFlagField IS_INNER = FlagField.booleanAfter(CLASS_KIND);
 
     // Callables
 
     // TODO: use these flags
-    public static final FlagField<Boolean> RESERVED_1 = FlagField.booleanAfter(MODALITY);
-    public static final FlagField<Boolean> RESERVED_2 = FlagField.booleanAfter(RESERVED_1);
+    public static final BooleanFlagField RESERVED_1 = FlagField.booleanAfter(MODALITY);
+    public static final BooleanFlagField RESERVED_2 = FlagField.booleanAfter(RESERVED_1);
 
     public static final FlagField<ProtoBuf.MemberKind> MEMBER_KIND = FlagField.after(RESERVED_2, ProtoBuf.MemberKind.values());
 
     // Constructors
 
-    public static final FlagField<Boolean> IS_SECONDARY = FlagField.booleanAfter(VISIBILITY);
+    public static final BooleanFlagField IS_SECONDARY = FlagField.booleanAfter(VISIBILITY);
 
     // Functions
 
-    public static final FlagField<Boolean> IS_OPERATOR = FlagField.booleanAfter(MEMBER_KIND);
-    public static final FlagField<Boolean> IS_INFIX = FlagField.booleanAfter(IS_OPERATOR);
+    public static final BooleanFlagField IS_OPERATOR = FlagField.booleanAfter(MEMBER_KIND);
+    public static final BooleanFlagField IS_INFIX = FlagField.booleanAfter(IS_OPERATOR);
 
     // Properties
 
-    public static final FlagField<Boolean> IS_VAR = FlagField.booleanAfter(MEMBER_KIND);
-    public static final FlagField<Boolean> HAS_GETTER = FlagField.booleanAfter(IS_VAR);
-    public static final FlagField<Boolean> HAS_SETTER = FlagField.booleanAfter(HAS_GETTER);
-    public static final FlagField<Boolean> IS_CONST = FlagField.booleanAfter(HAS_SETTER);
-    public static final FlagField<Boolean> IS_LATEINIT = FlagField.booleanAfter(IS_CONST);
-    public static final FlagField<Boolean> HAS_CONSTANT = FlagField.booleanAfter(IS_LATEINIT);
+    public static final BooleanFlagField IS_VAR = FlagField.booleanAfter(MEMBER_KIND);
+    public static final BooleanFlagField HAS_GETTER = FlagField.booleanAfter(IS_VAR);
+    public static final BooleanFlagField HAS_SETTER = FlagField.booleanAfter(HAS_GETTER);
+    public static final BooleanFlagField IS_CONST = FlagField.booleanAfter(HAS_SETTER);
+    public static final BooleanFlagField IS_LATEINIT = FlagField.booleanAfter(IS_CONST);
+    public static final BooleanFlagField HAS_CONSTANT = FlagField.booleanAfter(IS_LATEINIT);
 
     // Parameters
 
-    public static final FlagField<Boolean> DECLARES_DEFAULT_VALUE = FlagField.booleanAfter(HAS_ANNOTATIONS);
+    public static final BooleanFlagField DECLARES_DEFAULT_VALUE = FlagField.booleanAfter(HAS_ANNOTATIONS);
 
     // Accessors
 
     // It's important that this flag is negated: "is NOT default" instead of "is default"
-    public static final FlagField<Boolean> IS_NOT_DEFAULT = FlagField.booleanAfter(MODALITY);
+    public static final BooleanFlagField IS_NOT_DEFAULT = FlagField.booleanAfter(MODALITY);
 
     // ---
 
@@ -253,11 +254,11 @@ public class Flags {
             return new EnumLiteFlagField<E>(0, values);
         }
 
-        public static FlagField<Boolean> booleanFirst() {
+        public static BooleanFlagField booleanFirst() {
             return new BooleanFlagField(0);
         }
 
-        public static FlagField<Boolean> booleanAfter(FlagField<?> previousField) {
+        public static BooleanFlagField booleanAfter(FlagField<?> previousField) {
             int offset = previousField.offset + previousField.bitWidth;
             return new BooleanFlagField(offset);
         }
@@ -272,6 +273,7 @@ public class Flags {
             this.values = values;
         }
 
+        @Nullable
         public E get(int flags) {
             int maskUnshifted = (1 << bitWidth) - 1;
             int mask = maskUnshifted << offset;
@@ -281,7 +283,7 @@ public class Flags {
                     return e;
                 }
             }
-            throw new IllegalStateException("Flag not found: " + value);
+            return null;
         }
 
         public int toFlags(E value) {
@@ -292,7 +294,7 @@ public class Flags {
 
     }
 
-    private static class BooleanFlagField extends FlagField<Boolean> {
+    public static class BooleanFlagField extends FlagField<Boolean> {
         private static final Boolean[] BOOLEAN = { false, true };
 
         public BooleanFlagField(int offset) {
@@ -303,6 +305,13 @@ public class Flags {
         protected int getIntValue(Boolean value) {
             return value ? 1 : 0;
         }
+
+        @NotNull
+        @Override
+        public Boolean get(int flags) {
+            //noinspection ConstantConditions
+            return super.get(flags);
+        }
     }
 
     private static class EnumLiteFlagField<E extends Internal.EnumLite> extends FlagField<E> {
diff --git a/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/protoEnumMapping.kt b/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/protoEnumMapping.kt
index a0f1cbf0d2d..f0030c3b56e 100644
--- a/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/protoEnumMapping.kt
+++ b/core/deserialization/src/org/jetbrains/kotlin/serialization/deserialization/protoEnumMapping.kt
@@ -26,39 +26,43 @@ import org.jetbrains.kotlin.types.Variance
 
 object Deserialization {
     @JvmStatic
-    fun memberKind(memberKind: ProtoBuf.MemberKind) = when (memberKind) {
+    fun memberKind(memberKind: ProtoBuf.MemberKind?) = when (memberKind) {
         ProtoBuf.MemberKind.DECLARATION -> CallableMemberDescriptor.Kind.DECLARATION
         ProtoBuf.MemberKind.FAKE_OVERRIDE -> CallableMemberDescriptor.Kind.FAKE_OVERRIDE
         ProtoBuf.MemberKind.DELEGATION -> CallableMemberDescriptor.Kind.DELEGATION
         ProtoBuf.MemberKind.SYNTHESIZED -> CallableMemberDescriptor.Kind.SYNTHESIZED
+        else -> CallableMemberDescriptor.Kind.DECLARATION
     }
 
     @JvmStatic
-    fun modality(modality: ProtoBuf.Modality) = when (modality) {
+    fun modality(modality: ProtoBuf.Modality?) = when (modality) {
         ProtoBuf.Modality.FINAL -> Modality.FINAL
         ProtoBuf.Modality.OPEN -> Modality.OPEN
         ProtoBuf.Modality.ABSTRACT -> Modality.ABSTRACT
         ProtoBuf.Modality.SEALED -> Modality.SEALED
+        else -> Modality.FINAL
     }
 
     @JvmStatic
-    fun visibility(visibility: ProtoBuf.Visibility) = when (visibility) {
+    fun visibility(visibility: ProtoBuf.Visibility?) = when (visibility) {
         ProtoBuf.Visibility.INTERNAL -> Visibilities.INTERNAL
         ProtoBuf.Visibility.PRIVATE -> Visibilities.PRIVATE
         ProtoBuf.Visibility.PRIVATE_TO_THIS -> Visibilities.PRIVATE_TO_THIS
         ProtoBuf.Visibility.PROTECTED -> Visibilities.PROTECTED
         ProtoBuf.Visibility.PUBLIC -> Visibilities.PUBLIC
         ProtoBuf.Visibility.LOCAL -> Visibilities.LOCAL
+        else -> Visibilities.PRIVATE
     }
 
     @JvmStatic
-    fun classKind(kind: ProtoBuf.Class.Kind): ClassKind = when (kind) {
+    fun classKind(kind: ProtoBuf.Class.Kind?): ClassKind = when (kind) {
         ProtoBuf.Class.Kind.CLASS -> ClassKind.CLASS
         ProtoBuf.Class.Kind.INTERFACE -> ClassKind.INTERFACE
         ProtoBuf.Class.Kind.ENUM_CLASS -> ClassKind.ENUM_CLASS
         ProtoBuf.Class.Kind.ENUM_ENTRY -> ClassKind.ENUM_ENTRY
         ProtoBuf.Class.Kind.ANNOTATION_CLASS -> ClassKind.ANNOTATION_CLASS
         ProtoBuf.Class.Kind.OBJECT, ProtoBuf.Class.Kind.COMPANION_OBJECT -> ClassKind.OBJECT
+        else -> ClassKind.CLASS
     }
 
     @JvmStatic
@@ -66,6 +70,7 @@ object Deserialization {
         ProtoBuf.TypeParameter.Variance.IN -> Variance.IN_VARIANCE
         ProtoBuf.TypeParameter.Variance.OUT -> Variance.OUT_VARIANCE
         ProtoBuf.TypeParameter.Variance.INV -> Variance.INVARIANT
+        else -> Variance.INVARIANT
     }
 
     @JvmStatic
@@ -73,6 +78,8 @@ object Deserialization {
         ProtoBuf.Type.Argument.Projection.IN -> Variance.IN_VARIANCE
         ProtoBuf.Type.Argument.Projection.OUT -> Variance.OUT_VARIANCE
         ProtoBuf.Type.Argument.Projection.INV -> Variance.INVARIANT
-        else -> throw IllegalArgumentException("Only IN, OUT and INV are supported. Actual argument: $variance")
+        ProtoBuf.Type.Argument.Projection.STAR ->
+            throw IllegalArgumentException("Only IN, OUT and INV are supported. Actual argument: $variance")
+        else -> Variance.INVARIANT
     }
-}
\ No newline at end of file
+}