Allow command options to have nullable types and default values (#1444)

pkl-core/src/main/java/org/pkl/core/runtime/CommandSpecParser.java

@@ -513,12 +513,6 @@ public final class CommandSpecParser {
       var typeNode = resolved.getFirst();
       isNullable = resolved.getSecond();
       defaultValue = CommandSpecParser.this.getDefaultValue(prop, requireExplicitDefault);
-      if (isNullable && defaultValue != null) {
-        throw exceptionBuilder()
-            .evalError("commandOptionTypeNullableWithDefaultValue", prop.getName())
-            .withSourceSection(prop.getHeaderSection())
-            .build();
-      }
 
       resolve(prop, typeNode);
       return this;

pkl-core/src/main/resources/org/pkl/core/errorMessages.properties

@@ -1098,11 +1098,6 @@ Found both `@Flag` and `@Argument` annotations for options property `{0}`.\n\
 \n\
 Only one option type may be specified.
 
-commandOptionTypeNullableWithDefaultValue=\
-Unexpected option property `{0}` with nullable type and default value.\n\
-\n\
-Options with default values must not be nullable.
-
 commandOptionUnsupportedType=\
 Command option property `{0}` has unsupported {1}type `{2}`.
 

pkl-core/src/test/kotlin/org/pkl/core/runtime/CommandSpecParserTest.kt

@@ -292,26 +292,6 @@ class CommandSpecParserTest {
     assertThat(exc.message).contains("No type annotation found for `foo` property.")
   }
 
-  @Test
-  fun `nullable option with default not allowed`() {
-    val moduleUri =
-      writePklFile(
-        "cmd.pkl",
-        renderOptions +
-          """
-      class Options {
-        foo: String? = "bar"
-      }
-    """
-            .trimIndent(),
-      )
-
-    val exc = assertThrows<PklException> { parse(moduleUri) }
-    assertThat(exc.message).contains("foo: String? = \"bar\"")
-    assertThat(exc.message)
-      .contains("Unexpected option property `foo` with nullable type and default value")
-  }
-
   @Test
   fun `option with union type containing non-string-literals`() {
     val moduleUri =