Return error on failed conversion

Signed-off-by: Theo Despoudis <thdespou@hotmail.com>

Author: theodesp

sql/expression/function/sqrt_power.go

@@ -55,7 +55,7 @@ func (s *Sqrt) Eval(ctx *sql.Context, row sql.Row) (interface{}, error) {
 
 	child, err = sql.Float64.Convert(child)
 	if err != nil {
-		return nil, nil
+		return nil, err
 	}
 
 	return math.Sqrt(child.(float64)), nil

sql/expression/function/sqrt_power_test.go

@@ -20,7 +20,7 @@ func TestSqrt(t *testing.T) {
 		err      bool
 	}{
 		{"null input", sql.NewRow(nil), nil, false},
-		{"invalid string", sql.NewRow("foo"), nil, false},
+		{"invalid string", sql.NewRow("foo"), nil, true},
 		{"valid string", sql.NewRow("9"), float64(3), false},
 		{"number is zero", sql.NewRow(0), float64(0), false},
 		{"positive number", sql.NewRow(8), float64(2.8284271247461903), false},