diff --git a/CHANGELOG.md b/CHANGELOG.md
index 39ee157fd7..605608182c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -34,6 +34,7 @@ Thank you to all who have contributed!
 ### Deprecated
 
 ### Fixed
+- Return type of `partiql-ast`'s `SqlDialect` for `defaultReturn` to be a `SqlBlock` rather than `Nothing`
 
 ### Removed
 
@@ -41,7 +42,7 @@ Thank you to all who have contributed!
 
 ### Contributors
 Thank you to all who have contributed!
-- @<your-username>
+- @alancai98
 
 ## [0.14.2] - 2024-01-25
 
diff --git a/partiql-ast/src/main/kotlin/org/partiql/ast/sql/SqlDialect.kt b/partiql-ast/src/main/kotlin/org/partiql/ast/sql/SqlDialect.kt
index 05dc0a9610..bb77efa4c9 100644
--- a/partiql-ast/src/main/kotlin/org/partiql/ast/sql/SqlDialect.kt
+++ b/partiql-ast/src/main/kotlin/org/partiql/ast/sql/SqlDialect.kt
@@ -40,12 +40,12 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
         public val PARTIQL = object : SqlDialect() {}
     }
 
-    override fun defaultReturn(node: AstNode, head: SqlBlock) =
+    override fun defaultReturn(node: AstNode, head: SqlBlock): SqlBlock =
         throw UnsupportedOperationException("Cannot print $node")
 
     // STATEMENTS
 
-    override fun visitStatementQuery(node: Statement.Query, head: SqlBlock) = visitExpr(node.expr, head)
+    override fun visitStatementQuery(node: Statement.Query, head: SqlBlock): SqlBlock = visitExpr(node.expr, head)
 
     // IDENTIFIERS & PATHS
 
@@ -55,7 +55,7 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
      * @param node
      * @param head
      */
-    public open fun visitExprWrapped(node: Expr, head: SqlBlock) = when (node) {
+    public open fun visitExprWrapped(node: Expr, head: SqlBlock): SqlBlock = when (node) {
         is Expr.SFW -> {
             var h = head
             h = h concat "("
@@ -66,7 +66,7 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
         else -> visitExpr(node, head)
     }
 
-    override fun visitIdentifierSymbol(node: Identifier.Symbol, head: SqlBlock) = head concat r(node.sql())
+    override fun visitIdentifierSymbol(node: Identifier.Symbol, head: SqlBlock): SqlBlock = head concat r(node.sql())
 
     override fun visitIdentifierQualified(node: Identifier.Qualified, head: SqlBlock): SqlBlock {
         val path = node.steps.fold(node.root.sql()) { p, step -> p + "." + step.sql() }
@@ -116,93 +116,93 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
     }
 
     // cannot write path step outside the context of a path as we don't want it to reflow
-    override fun visitPathStep(node: Path.Step, head: SqlBlock) = error("path step cannot be written directly")
+    override fun visitPathStep(node: Path.Step, head: SqlBlock): SqlBlock = error("path step cannot be written directly")
 
-    override fun visitPathStepSymbol(node: Path.Step.Symbol, head: SqlBlock) = visitPathStep(node, head)
+    override fun visitPathStepSymbol(node: Path.Step.Symbol, head: SqlBlock): SqlBlock = visitPathStep(node, head)
 
-    override fun visitPathStepIndex(node: Path.Step.Index, head: SqlBlock) = visitPathStep(node, head)
+    override fun visitPathStepIndex(node: Path.Step.Index, head: SqlBlock): SqlBlock = visitPathStep(node, head)
 
     // TYPES
 
-    override fun visitTypeNullType(node: Type.NullType, head: SqlBlock) = head concat r("NULL")
+    override fun visitTypeNullType(node: Type.NullType, head: SqlBlock): SqlBlock = head concat r("NULL")
 
-    override fun visitTypeMissing(node: Type.Missing, head: SqlBlock) = head concat r("MISSING")
+    override fun visitTypeMissing(node: Type.Missing, head: SqlBlock): SqlBlock = head concat r("MISSING")
 
-    override fun visitTypeBool(node: Type.Bool, head: SqlBlock) = head concat r("BOOL")
+    override fun visitTypeBool(node: Type.Bool, head: SqlBlock): SqlBlock = head concat r("BOOL")
 
-    override fun visitTypeTinyint(node: Type.Tinyint, head: SqlBlock) = head concat r("TINYINT")
+    override fun visitTypeTinyint(node: Type.Tinyint, head: SqlBlock): SqlBlock = head concat r("TINYINT")
 
-    override fun visitTypeSmallint(node: Type.Smallint, head: SqlBlock) = head concat r("SMALLINT")
+    override fun visitTypeSmallint(node: Type.Smallint, head: SqlBlock): SqlBlock = head concat r("SMALLINT")
 
-    override fun visitTypeInt2(node: Type.Int2, head: SqlBlock) = head concat r("INT2")
+    override fun visitTypeInt2(node: Type.Int2, head: SqlBlock): SqlBlock = head concat r("INT2")
 
-    override fun visitTypeInt4(node: Type.Int4, head: SqlBlock) = head concat r("INT4")
+    override fun visitTypeInt4(node: Type.Int4, head: SqlBlock): SqlBlock = head concat r("INT4")
 
-    override fun visitTypeBigint(node: Type.Bigint, head: SqlBlock) = head concat r("BIGINT")
+    override fun visitTypeBigint(node: Type.Bigint, head: SqlBlock): SqlBlock = head concat r("BIGINT")
 
-    override fun visitTypeInt8(node: Type.Int8, head: SqlBlock) = head concat r("INT8")
+    override fun visitTypeInt8(node: Type.Int8, head: SqlBlock): SqlBlock = head concat r("INT8")
 
-    override fun visitTypeInt(node: Type.Int, head: SqlBlock) = head concat r("INT")
+    override fun visitTypeInt(node: Type.Int, head: SqlBlock): SqlBlock = head concat r("INT")
 
-    override fun visitTypeReal(node: Type.Real, head: SqlBlock) = head concat r("REAL")
+    override fun visitTypeReal(node: Type.Real, head: SqlBlock): SqlBlock = head concat r("REAL")
 
-    override fun visitTypeFloat32(node: Type.Float32, head: SqlBlock) = head concat r("FLOAT32")
+    override fun visitTypeFloat32(node: Type.Float32, head: SqlBlock): SqlBlock = head concat r("FLOAT32")
 
-    override fun visitTypeFloat64(node: Type.Float64, head: SqlBlock) = head concat r("DOUBLE PRECISION")
+    override fun visitTypeFloat64(node: Type.Float64, head: SqlBlock): SqlBlock = head concat r("DOUBLE PRECISION")
 
-    override fun visitTypeDecimal(node: Type.Decimal, head: SqlBlock) =
+    override fun visitTypeDecimal(node: Type.Decimal, head: SqlBlock): SqlBlock =
         head concat type("DECIMAL", node.precision, node.scale)
 
-    override fun visitTypeNumeric(node: Type.Numeric, head: SqlBlock) =
+    override fun visitTypeNumeric(node: Type.Numeric, head: SqlBlock): SqlBlock =
         head concat type("NUMERIC", node.precision, node.scale)
 
-    override fun visitTypeChar(node: Type.Char, head: SqlBlock) = head concat type("CHAR", node.length)
+    override fun visitTypeChar(node: Type.Char, head: SqlBlock): SqlBlock = head concat type("CHAR", node.length)
 
-    override fun visitTypeVarchar(node: Type.Varchar, head: SqlBlock) = head concat type("VARCHAR", node.length)
+    override fun visitTypeVarchar(node: Type.Varchar, head: SqlBlock): SqlBlock = head concat type("VARCHAR", node.length)
 
-    override fun visitTypeString(node: Type.String, head: SqlBlock) = head concat r("STRING")
+    override fun visitTypeString(node: Type.String, head: SqlBlock): SqlBlock = head concat r("STRING")
 
-    override fun visitTypeSymbol(node: Type.Symbol, head: SqlBlock) = head concat r("SYMBOL")
+    override fun visitTypeSymbol(node: Type.Symbol, head: SqlBlock): SqlBlock = head concat r("SYMBOL")
 
-    override fun visitTypeBit(node: Type.Bit, head: SqlBlock) = head concat type("BIT", node.length)
+    override fun visitTypeBit(node: Type.Bit, head: SqlBlock): SqlBlock = head concat type("BIT", node.length)
 
-    override fun visitTypeBitVarying(node: Type.BitVarying, head: SqlBlock) = head concat type("BINARY", node.length)
+    override fun visitTypeBitVarying(node: Type.BitVarying, head: SqlBlock): SqlBlock = head concat type("BINARY", node.length)
 
-    override fun visitTypeByteString(node: Type.ByteString, head: SqlBlock) = head concat type("BYTE", node.length)
+    override fun visitTypeByteString(node: Type.ByteString, head: SqlBlock): SqlBlock = head concat type("BYTE", node.length)
 
-    override fun visitTypeBlob(node: Type.Blob, head: SqlBlock) = head concat type("BLOB", node.length)
+    override fun visitTypeBlob(node: Type.Blob, head: SqlBlock): SqlBlock = head concat type("BLOB", node.length)
 
-    override fun visitTypeClob(node: Type.Clob, head: SqlBlock) = head concat type("CLOB", node.length)
+    override fun visitTypeClob(node: Type.Clob, head: SqlBlock): SqlBlock = head concat type("CLOB", node.length)
 
-    override fun visitTypeBag(node: Type.Bag, head: SqlBlock) = head concat r("BAG")
+    override fun visitTypeBag(node: Type.Bag, head: SqlBlock): SqlBlock = head concat r("BAG")
 
-    override fun visitTypeList(node: Type.List, head: SqlBlock) = head concat r("LIST")
+    override fun visitTypeList(node: Type.List, head: SqlBlock): SqlBlock = head concat r("LIST")
 
-    override fun visitTypeSexp(node: Type.Sexp, head: SqlBlock) = head concat r("SEXP")
+    override fun visitTypeSexp(node: Type.Sexp, head: SqlBlock): SqlBlock = head concat r("SEXP")
 
-    override fun visitTypeTuple(node: Type.Tuple, head: SqlBlock) = head concat r("TUPLE")
+    override fun visitTypeTuple(node: Type.Tuple, head: SqlBlock): SqlBlock = head concat r("TUPLE")
 
-    override fun visitTypeStruct(node: Type.Struct, head: SqlBlock) = head concat r("STRUCT")
+    override fun visitTypeStruct(node: Type.Struct, head: SqlBlock): SqlBlock = head concat r("STRUCT")
 
-    override fun visitTypeAny(node: Type.Any, head: SqlBlock) = head concat r("ANY")
+    override fun visitTypeAny(node: Type.Any, head: SqlBlock): SqlBlock = head concat r("ANY")
 
-    override fun visitTypeDate(node: Type.Date, head: SqlBlock) = head concat r("DATE")
+    override fun visitTypeDate(node: Type.Date, head: SqlBlock): SqlBlock = head concat r("DATE")
 
     override fun visitTypeTime(node: Type.Time, head: SqlBlock): SqlBlock = head concat type("TIME", node.precision)
 
-    override fun visitTypeTimeWithTz(node: Type.TimeWithTz, head: SqlBlock) =
+    override fun visitTypeTimeWithTz(node: Type.TimeWithTz, head: SqlBlock): SqlBlock =
         head concat type("TIME WITH TIMEZONE", node.precision, gap = true)
 
-    override fun visitTypeTimestamp(node: Type.Timestamp, head: SqlBlock) =
+    override fun visitTypeTimestamp(node: Type.Timestamp, head: SqlBlock): SqlBlock =
         head concat type("TIMESTAMP", node.precision)
 
-    override fun visitTypeTimestampWithTz(node: Type.TimestampWithTz, head: SqlBlock) =
+    override fun visitTypeTimestampWithTz(node: Type.TimestampWithTz, head: SqlBlock): SqlBlock =
         head concat type("TIMESTAMP WITH TIMEZONE", node.precision, gap = true)
 
-    override fun visitTypeInterval(node: Type.Interval, head: SqlBlock) = head concat type("INTERVAL", node.precision)
+    override fun visitTypeInterval(node: Type.Interval, head: SqlBlock): SqlBlock = head concat type("INTERVAL", node.precision)
 
     // unsupported
-    override fun visitTypeCustom(node: Type.Custom, head: SqlBlock) = defaultReturn(node, head)
+    override fun visitTypeCustom(node: Type.Custom, head: SqlBlock): SqlBlock = defaultReturn(node, head)
 
     // Expressions
 
@@ -274,7 +274,7 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
         return h
     }
 
-    override fun visitExprSessionAttribute(node: Expr.SessionAttribute, head: SqlBlock) =
+    override fun visitExprSessionAttribute(node: Expr.SessionAttribute, head: SqlBlock): SqlBlock =
         head concat r(node.attribute.name)
 
     override fun visitExprPath(node: Expr.Path, head: SqlBlock): SqlBlock {
@@ -283,7 +283,7 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
         return h
     }
 
-    override fun visitExprPathStepSymbol(node: Expr.Path.Step.Symbol, head: SqlBlock) =
+    override fun visitExprPathStepSymbol(node: Expr.Path.Step.Symbol, head: SqlBlock): SqlBlock =
         head concat r(".${node.symbol.sql()}")
 
     override fun visitExprPathStepIndex(node: Expr.Path.Step.Index, head: SqlBlock): SqlBlock {
@@ -296,9 +296,9 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
         return h
     }
 
-    override fun visitExprPathStepWildcard(node: Expr.Path.Step.Wildcard, head: SqlBlock) = head concat r("[*]")
+    override fun visitExprPathStepWildcard(node: Expr.Path.Step.Wildcard, head: SqlBlock): SqlBlock = head concat r("[*]")
 
-    override fun visitExprPathStepUnpivot(node: Expr.Path.Step.Unpivot, head: SqlBlock) = head concat r(".*")
+    override fun visitExprPathStepUnpivot(node: Expr.Path.Step.Unpivot, head: SqlBlock): SqlBlock = head concat r(".*")
 
     override fun visitExprCall(node: Expr.Call, head: SqlBlock): SqlBlock {
         var h = head
@@ -320,11 +320,11 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
         return h
     }
 
-    override fun visitExprParameter(node: Expr.Parameter, head: SqlBlock) = head concat r("?")
+    override fun visitExprParameter(node: Expr.Parameter, head: SqlBlock): SqlBlock = head concat r("?")
 
-    override fun visitExprValues(node: Expr.Values, head: SqlBlock) = head concat list("VALUES (") { node.rows }
+    override fun visitExprValues(node: Expr.Values, head: SqlBlock): SqlBlock = head concat list("VALUES (") { node.rows }
 
-    override fun visitExprValuesRow(node: Expr.Values.Row, head: SqlBlock) = head concat list { node.items }
+    override fun visitExprValuesRow(node: Expr.Values.Row, head: SqlBlock): SqlBlock = head concat list { node.items }
 
     override fun visitExprCollection(node: Expr.Collection, head: SqlBlock): SqlBlock {
         val (start, end) = when (node.type) {
@@ -337,7 +337,7 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
         return head concat list(start, end) { node.values }
     }
 
-    override fun visitExprStruct(node: Expr.Struct, head: SqlBlock) = head concat list("{", "}") { node.fields }
+    override fun visitExprStruct(node: Expr.Struct, head: SqlBlock): SqlBlock = head concat list("{", "}") { node.fields }
 
     override fun visitExprStructField(node: Expr.Struct.Field, head: SqlBlock): SqlBlock {
         var h = head
@@ -698,7 +698,7 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
 
     // LET
 
-    override fun visitLet(node: Let, head: SqlBlock) = head concat list("LET ", "") { node.bindings }
+    override fun visitLet(node: Let, head: SqlBlock): SqlBlock = head concat list("LET ", "") { node.bindings }
 
     override fun visitLetBinding(node: Let.Binding, head: SqlBlock): SqlBlock {
         var h = head
@@ -750,7 +750,7 @@ public abstract class SqlDialect : AstBaseVisitor<SqlBlock, SqlBlock>() {
 
     // ORDER BY
 
-    override fun visitOrderBy(node: OrderBy, head: SqlBlock) = head concat list("ORDER BY ", "") { node.sorts }
+    override fun visitOrderBy(node: OrderBy, head: SqlBlock): SqlBlock = head concat list("ORDER BY ", "") { node.sorts }
 
     override fun visitSort(node: Sort, head: SqlBlock): SqlBlock {
         var h = head