fix(lapis): render empty Or and And as valid SaneQL

lapis/src/main/kotlin/org/genspectrum/lapis/rhydb/SaneQlAst.kt

@@ -94,21 +94,29 @@ data class SaneQlNot(
 }
 
 /**
- * Variadic `&&` conjunction.
+ * Variadic `&&` conjunction. Without children, it is `true`.
  */
 data class SaneQlAnd(
     val children: List<SaneQlExpression>,
 ) : SaneQlExpression {
-    override fun render() = children.joinToString(" && ") { wrapIfNeeded(it) }
+    override fun render() =
+        when {
+            children.isEmpty() -> "true"
+            else -> children.joinToString(" && ") { wrapIfNeeded(it) }
+        }
 }
 
 /**
- * Variadic `||` disjunction.
+ * Variadic `||` disjunction. Without children (e.g. for a filter by an empty list), it is `false`.
  */
 data class SaneQlOr(
     val children: List<SaneQlExpression>,
 ) : SaneQlExpression {
-    override fun render() = children.joinToString(" || ") { wrapIfNeeded(it) }
+    override fun render() =
+        when {
+            children.isEmpty() -> "false"
+            else -> children.joinToString(" || ") { wrapIfNeeded(it) }
+        }
 }
 
 private fun wrapIfNeeded(expression: SaneQlExpression): String {

lapis/src/test/kotlin/org/genspectrum/lapis/rhydb/RhyDbQueryToSaneQlTest.kt

@@ -455,6 +455,16 @@ class RhyDbQueryToSaneQlTest {
                     Or(StringEquals("theColumn", "theValue"), StringEquals("theOtherColumn", "theOtherValue")),
                     """"theColumn" = 'theValue' || "theOtherColumn" = 'theOtherValue'""",
                 ),
+                // Empty Or, e.g. from a filter by an empty list
+                Arguments.of(
+                    Or(emptyList()),
+                    "false",
+                ),
+                // Empty And
+                Arguments.of(
+                    And(emptyList()),
+                    "true",
+                ),
                 // Not
                 Arguments.of(
                     Not(StringEquals("theColumn", "theValue")),

lapis/src/test/kotlin/org/genspectrum/lapis/rhydb/SaneQlAstTest.kt

@@ -109,6 +109,22 @@ class SaneQlAstTest {
         assertThat(or.render(), equalTo("(true && false) || true"))
     }
 
+    @Test
+    fun `GIVEN empty or THEN renders false`() {
+        assertThat(SaneQlOr(emptyList()).render(), equalTo("false"))
+    }
+
+    @Test
+    fun `GIVEN empty and THEN renders true`() {
+        assertThat(SaneQlAnd(emptyList()).render(), equalTo("true"))
+    }
+
+    @Test
+    fun `GIVEN and with empty or child THEN renders valid SaneQL`() {
+        val and = SaneQlAnd(listOf(SaneQlOr(emptyList()), SaneQlBoolean(true)))
+        assertThat(and.render(), equalTo("(false) && true"))
+    }
+
     @Test
     fun `GIVEN and with flat non-and-or children THEN does not add parentheses`() {
         val and = SaneQlAnd(listOf(SaneQlBoolean(true), SaneQlBoolean(false)))