fix: handle null decimals and improve error reporting in DecimalColumn

Author: RaphDal

buffer.go

@@ -581,12 +581,12 @@ func (b *buffer) DecimalColumn(name string, val any) *buffer {
 	if b.lastErr != nil {
 		return b
 	}
-	b.WriteByte('=')
 	if str, ok := val.(string); ok {
 		if err := validateDecimalText(str); err != nil {
 			b.lastErr = err
 			return b
 		}
+		b.WriteByte('=')
 		b.WriteString(str)
 		b.WriteByte('d')
 		b.hasFields = true
@@ -603,6 +603,11 @@ func (b *buffer) DecimalColumn(name string, val any) *buffer {
 		b.lastErr = err
 		return b
 	}
+	if len(payload) == 0 {
+		// Don't write null decimals
+		return b
+	}
+	b.WriteByte('=')
 	b.WriteByte('=')
 	b.WriteByte(decimalBinaryTypeCode)
 	b.WriteByte(scale)

buffer_test.go

@@ -618,6 +618,13 @@ func TestDecimalColumnErrors(t *testing.T) {
 		assert.ErrorContains(t, err, "unsupported decimal column value type")
 		assert.Empty(t, buf.Messages())
 	})
+
+	t.Run("no column", func(t *testing.T) {
+		buf := newTestBuffer()
+		err := buf.Table(testTable).DecimalColumn("price", qdb.NullDecimal()).At(time.Time{}, false)
+		assert.ErrorContains(t, err, "no symbols or columns were provided: invalid message")
+		assert.Empty(t, buf.Messages())
+	})
 }
 
 func TestFloat64Array1DColumn(t *testing.T) {