Minor type inference fixes to do with null and bottom types.

pkg/front_end/test/fasta/strong.status

Index: pkg/front_end/test/fasta/strong.status
diff --git a/pkg/front_end/test/fasta/strong.status b/pkg/front_end/test/fasta/strong.status
index 909b6e38d73d5f20be553cf108a2d700b736931c..523651089d01a822aa51cd3c4a5431c0de3fa86d 100644
--- a/pkg/front_end/test/fasta/strong.status
+++ b/pkg/front_end/test/fasta/strong.status
@@ -63,12 +63,8 @@ inference/block_bodied_lambdas_async_all_returns_are_values: Fail
 inference/block_bodied_lambdas_async_mix_of_values_and_futures: Fail
 inference/block_bodied_lambdas_async_star: Fail
 inference/block_bodied_lambdas_downwards_incompatible_with_upwards_inference: Fail
-inference/block_bodied_lambdas_infer_bottom_async: Fail
-inference/block_bodied_lambdas_infer_bottom_async_star: Fail
 inference/block_bodied_lambdas_infer_bottom_sync: Fail
-inference/block_bodied_lambdas_infer_bottom_sync_star: Fail
 inference/block_bodied_lambdas_lub: Fail
-inference/block_bodied_lambdas_no_return: Fail
 inference/block_bodied_lambdas_sync_star: Fail
 inference/circular_reference_via_closures: Fail
 inference/circular_reference_via_closures_initializer_types: Fail
@@ -153,14 +149,12 @@ inference/infer_statics_transitively: Fail
 inference/infer_statics_transitively3: Fail
 inference/infer_statics_transitively_a: Fail
 inference/infer_statics_with_method_invocations: Fail
-inference/infer_throw: Fail
 inference/infer_type_on_var_from_field: Fail
 inference/infer_typed_map_literal: Fail
 inference/infer_types_on_generic_instantiations_in_library_cycle: Fail
 inference/infer_types_on_loop_indices_for_each_loop: Fail
 inference/infer_types_on_loop_indices_for_loop_with_inference: Fail
 inference/inferred_nonstatic_field_depends_on_static_field_complex: Fail
-inference/inferred_type_block_closure_no_args_no_return: Fail
 inference/inferred_type_cascade: Fail
 inference/inferred_type_extract_method_tear_off: Fail
 inference/inferred_type_extract_method_tear_off_via_interface: Fail
@@ -185,8 +179,6 @@ inference/reference_to_typedef: Fail
 inference/refine_binary_expression_type_type_parameter_t_double: Fail
 inference/refine_binary_expression_type_type_parameter_t_int: Fail
 inference/refine_binary_expression_type_type_parameter_t_t: Fail
-inference/type_promotion_stopped_by_access_in_a_closure: Fail
-inference/type_promotion_stopped_by_mutation_in_a_closure: Fail
 inference/unsafe_block_closure_inference_closure_call: Fail
 inference/unsafe_block_closure_inference_function_call_explicit_dynamic_param_via_expr1: Fail
 inference/unsafe_block_closure_inference_function_call_explicit_type_param_via_expr1: Fail