DfaBoxedValue#createUnboxed: disable for non-primitive constants (e.g. strings)

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/value/DfaBoxedValue.java

@@ -15,12 +15,13 @@
  */
 package com.intellij.codeInspection.dataFlow.value;
 
+import com.intellij.psi.util.TypeConversionUtil;
 import com.intellij.util.containers.ContainerUtil;
-import java.util.HashMap;
 import org.jetbrains.annotations.NonNls;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
+import java.util.HashMap;
 import java.util.Map;
 
 public class DfaBoxedValue extends DfaValue {
@@ -70,8 +71,7 @@ public class DfaBoxedValue extends DfaValue {
         return ((DfaBoxedValue)value).getWrappedValue();
       }
       if (value instanceof DfaConstValue) {
-        if (value == value.myFactory.getConstFactory().getNull()) return DfaUnknownValue.getInstance();
-        return value;
+        return TypeConversionUtil.isPrimitiveAndNotNull(((DfaConstValue)value).getType()) ? value : DfaUnknownValue.getInstance();
       }
       if (value instanceof DfaVariableValue) {
         DfaVariableValue var = (DfaVariableValue)value;

java/java-tests/testData/inspection/dataFlow/fixture/BoxingIncorrectLiteral.java

@@ -0,0 +1,5 @@
+class Testcase {
+  void test() {
+    <error descr="Incompatible types. Found: 'java.lang.String', required: 'java.lang.Character'">Character x = "foo";</error>
+  }
+}

java/java-tests/testSrc/com/intellij/java/codeInspection/DataFlowInspectionTest.java

@@ -640,4 +640,5 @@ public class DataFlowInspectionTest extends DataFlowInspectionTestCase {
   public void testStringEquality() { doTest(); }
   public void testAssignmentFieldAliasing() { doTest(); }
   public void testNewBoxedNumberEquality() { doTest(); }
+  public void testBoxingIncorrectLiteral() { doTest(); }
 }