Reduce usage of Object#not_nil!

spec/ameba/ast/variabling/assignment_spec.cr

@@ -53,8 +53,8 @@ module Ameba::AST
         scope = Scope.new nodes.def_nodes.first
         variable = Variable.new(nodes.var_nodes.first, scope)
         assignment = Assignment.new(nodes.assign_nodes.first, variable, scope)
-        assignment.branch.should_not be_nil
+        branch = assignment.branch.should_not be_nil
-        assignment.branch.not_nil!.node.class.should eq Crystal::Expressions
+        branch.node.class.should eq Crystal::Expressions
       end
 
       it "returns inner branch" do
@@ -70,8 +70,8 @@ module Ameba::AST
         scope = Scope.new nodes.def_nodes.first
         variable = Variable.new(nodes.var_nodes.first, scope)
         assignment = Assignment.new(nodes.assign_nodes.first, variable, scope)
-        assignment.branch.should_not be_nil
+        branch = assignment.branch.should_not be_nil
-        assignment.branch.not_nil!.node.class.should eq Crystal::Assign
+        branch.node.class.should eq Crystal::Assign
       end
 
       it "returns nil if assignment does not have a branch" do

spec/ameba/cli/cmd_spec.cr

@@ -91,9 +91,8 @@ module Ameba::Cli
       describe "-e/--explain" do
         it "configures file/line/column" do
           c = Cli.parse_args %w(--explain src/file.cr:3:5)
-          c.location_to_explain.should_not be_nil
 
-          location_to_explain = c.location_to_explain.not_nil!
+          location_to_explain = c.location_to_explain.should_not be_nil
           location_to_explain[:file].should eq "src/file.cr"
           location_to_explain[:line].should eq 3
           location_to_explain[:column].should eq 5
@@ -154,9 +153,8 @@ module Ameba::Cli
 
       it "accepts one unknown arg as explain location if it has correct format" do
         c = Cli.parse_args %w(source.cr:3:22)
-        c.location_to_explain.should_not be_nil
 
-        location_to_explain = c.location_to_explain.not_nil!
+        location_to_explain = c.location_to_explain.should_not be_nil
         location_to_explain[:file].should eq "source.cr"
         location_to_explain[:line].should eq 3
         location_to_explain[:column].should eq 22

spec/ameba/config_spec.cr

@@ -165,7 +165,7 @@ module Ameba
       it "updates enabled property" do
         name = DummyRule.rule_name
         config.update_rule name, enabled: false
-        rule = config.rules.find(&.name.== name).not_nil!
+        rule = config.rules.find!(&.name.== name)
         rule.enabled.should be_false
       end
 
@@ -173,7 +173,7 @@ module Ameba
         name = DummyRule.rule_name
         excluded = %w(spec/source.cr)
         config.update_rule name, excluded: excluded
-        rule = config.rules.find(&.name.== name).not_nil!
+        rule = config.rules.find!(&.name.== name)
         rule.excluded.should eq excluded
       end
     end
@@ -184,7 +184,7 @@ module Ameba
       it "updates multiple rules by enabled property" do
         name = DummyRule.rule_name
         config.update_rules [name], enabled: false
-        rule = config.rules.find(&.name.== name).not_nil!
+        rule = config.rules.find!(&.name.== name)
         rule.enabled.should be_false
       end
 
@@ -192,14 +192,14 @@ module Ameba
         name = DummyRule.rule_name
         excluded = %w(spec/source.cr)
         config.update_rules [name], excluded: excluded
-        rule = config.rules.find(&.name.== name).not_nil!
+        rule = config.rules.find!(&.name.== name)
         rule.excluded.should eq excluded
       end
 
       it "updates a group of rules by enabled property" do
         group = DummyRule.group_name
         config.update_rules [group], enabled: false
-        rule = config.rules.find(&.name.== DummyRule.rule_name).not_nil!
+        rule = config.rules.find!(&.name.== DummyRule.rule_name)
         rule.enabled.should be_false
       end
 
@@ -207,7 +207,7 @@ module Ameba
         name = DummyRule.group_name
         excluded = %w(spec/source.cr)
         config.update_rules [name], excluded: excluded
-        rule = config.rules.find(&.name.== DummyRule.rule_name).not_nil!
+        rule = config.rules.find!(&.name.== DummyRule.rule_name)
         rule.excluded.should eq excluded
       end
     end

src/ameba/rule/style/redundant_next.cr

@@ -114,7 +114,7 @@ module Ameba::Rule::Style
 
     def test(source, node : Crystal::Next, visitor : AST::RedundantControlExpressionVisitor)
       return if allow_multi_next && node.exp.is_a?(Crystal::TupleLiteral)
-      return if allow_empty_next && (node.exp.nil? || node.exp.not_nil!.nop?)
+      return if allow_empty_next && (node.exp.nil? || node.exp.try(&.nop?))
 
       if (exp_code = control_exp_code(node, source.lines))
         issue_for node, MSG do |corrector|

src/ameba/rule/style/redundant_return.cr

@@ -111,7 +111,7 @@ module Ameba::Rule::Style
 
     def test(source, node : Crystal::Return, visitor : AST::RedundantControlExpressionVisitor)
       return if allow_multi_return && node.exp.is_a?(Crystal::TupleLiteral)
-      return if allow_empty_return && (node.exp.nil? || node.exp.not_nil!.nop?)
+      return if allow_empty_return && (node.exp.nil? || node.exp.try(&.nop?))
 
       if (exp_code = control_exp_code(node, source.lines))
         issue_for node, MSG do |corrector|