Nullability of error types is not known

#KT-6829 Fixed

compiler/frontend.java/src/org/jetbrains/kotlin/load/kotlin/KotlinJvmCheckerProvider.kt

@@ -152,13 +152,13 @@ private fun checkTypeParameterDescriptorsAreNotReified(
 
 public class JavaNullabilityWarningsChecker : AdditionalTypeChecker {
     private fun JetType.mayBeNull(): NullabilityInformationSource? {
-        if (!isFlexible() && TypeUtils.isNullableType(this)) return NullabilityInformationSource.KOTLIN
+        if (!isError() && !isFlexible() && TypeUtils.isNullableType(this)) return NullabilityInformationSource.KOTLIN
         if (getAnnotations().isMarkedNullable()) return NullabilityInformationSource.JAVA
         return null
     }
 
     private fun JetType.mustNotBeNull(): NullabilityInformationSource? {
-        if (!isFlexible() && !TypeUtils.isNullableType(this)) return NullabilityInformationSource.KOTLIN
+        if (!isError() && !isFlexible() && !TypeUtils.isNullableType(this)) return NullabilityInformationSource.KOTLIN
         if (!isMarkedNullable() && getAnnotations().isMarkedNotNull()) return NullabilityInformationSource.JAVA
         return null
     }

compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/kt6829.kt

@@ -0,0 +1,27 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+// KT-6829 False warning on map to @Nullable
+
+// FILE: p/J.java
+package p;
+
+import org.jetbrains.annotations.*;
+
+public class J {
+
+    @Nullable
+    public String method() { return ""; }
+}
+
+// FILE: k.kt
+
+import p.*
+
+fun foo(collection: Collection<J>) {
+    val mapped = collection.map { it.method() }
+    <!NULLABILITY_MISMATCH_BASED_ON_JAVA_ANNOTATIONS!>mapped[0]<!>.length()
+}
+
+public fun <T, R> Iterable<T>.map(transform: (T) -> R): List<R> {
+    null!!
+}

compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/kt6829.txt

@@ -0,0 +1,4 @@
+package
+
+internal fun foo(/*0*/ collection: kotlin.Collection<p.J>): kotlin.Unit
+public fun </*0*/ T, /*1*/ R> kotlin.Iterable<T>.map(/*0*/ transform: (T) -> R): kotlin.List<R>

compiler/tests/org/jetbrains/kotlin/checkers/JetDiagnosticsTestGenerated.java

@@ -8923,6 +8923,12 @@ public class JetDiagnosticsTestGenerated extends AbstractJetDiagnosticsTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("kt6829.kt")
+                public void testKt6829() throws Exception {
+                    String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/kt6829.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("multiDeclaration.kt")
                 public void testMultiDeclaration() throws Exception {
                     String fileName = JetTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/platformTypes/nullabilityWarnings/multiDeclaration.kt");