contract nulls are compatible with array return types (IDEA-137323)

java/java-analysis-impl/src/com/intellij/codeInspection/dataFlow/InferenceFromSourceUtil.java

@@ -65,7 +65,7 @@ public class InferenceFromSourceUtil {
              returnValue == MethodContract.ValueConstraint.FALSE_VALUE;
     }
 
-    if (returnType instanceof PsiClassType) {
+    if (!(returnType instanceof PsiPrimitiveType)) {
       return returnValue == MethodContract.ValueConstraint.NULL_VALUE ||
              returnValue == MethodContract.ValueConstraint.NOT_NULL_VALUE;
     }

java/java-tests/testData/inspection/dataFlow/contractCheck/ReturnPrimitiveArray.java

@@ -0,0 +1,10 @@
+import org.jetbrains.annotations.Contract;
+
+class Zoo {
+  @Contract( "null->null" )
+  static byte[] bar( String s )
+  {
+    if ( s == null )
+      return null;
+    return new byte[0];
+  }}

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

@@ -42,4 +42,5 @@ public class ContractCheckTest extends LightCodeInsightFixtureTestCase {
   public void testSignatureIssues() { doTest(); }
   public void testVarargInferred() { doTest(); }
   public void testDoubleParameter() { doTest(); }
+  public void testReturnPrimitiveArray() { doTest(); }
 }