don't evaluate an empty connection body

There's a required field now, so evaluating an empty block will always
fail.

terraform/eval_apply.go

@@ -494,17 +494,21 @@ func (n *EvalApplyProvisioners) apply(ctx EvalContext, provs []*configs.Provisio
 			connBody = baseConn
 		case localConn != nil:
 			connBody = localConn
-		default: // both are nil, by elimination
-			connBody = hcl.EmptyBody()
 		}
 
-		connInfo, _, connInfoDiags := ctx.EvaluateBlock(connBody, connectionBlockSupersetSchema, instanceAddr, keyData)
+		// start with an empty connInfo
+		connInfo := cty.NullVal(connectionBlockSupersetSchema.ImpliedType())
+
+		if connBody != nil {
+			var connInfoDiags tfdiags.Diagnostics
+			connInfo, _, connInfoDiags = ctx.EvaluateBlock(connBody, connectionBlockSupersetSchema, instanceAddr, keyData)
 			diags = diags.Append(connInfoDiags)
 			if diags.HasErrors() {
 				// "on failure continue" setting only applies to failures of the
 				// provisioner itself, not to invalid configuration.
 				return diags.Err()
 			}
+		}
 
 		{
 			// Call pre hook